...
platform :ios, '11.0'

pod "CleverTap-iOS-SDK", '5.2.1'
...
target 'NotificationService' do
  pod 'CTNotificationService', :modular_headers => true  
end

target 'NotificationContent' do
  pod "CTNotificationContent"
end

#import <CTNotificationService/CTNotificationService.h>

@interface NotificationService : CTNotificationServiceExtension

@end

#import "NotificationService.h"
#import "CleverTap.h"

@interface NotificationService ()

@property (nonatomic, strong) void (^contentHandler)(UNNotificationContent *contentToDeliver);
@property (nonatomic, strong) UNMutableNotificationContent *bestAttemptContent;

@end

@implementation NotificationService

- (void)didReceiveNotificationRequest:(UNNotificationRequest *)request withContentHandler:(void (^)(UNNotificationContent * _Nonnull))contentHandler {
    self.contentHandler = contentHandler;
    self.bestAttemptContent = [request.content mutableCopy];
    
    // Modify the notification content here...
    self.bestAttemptContent.title = [NSString stringWithFormat:@"%@ [modified]", self.bestAttemptContent.title];
//    
   self.contentHandler(self.bestAttemptContent);
    #if DEBUG
        NSLog(@"AppDelegate: didReceiveRemoteNotificationRequest!");
    #endif

    [[CleverTap sharedInstance] recordNotificationViewedEventWithData:request.content.userInfo];
    [super didReceiveNotificationRequest:request withContentHandler:contentHandler];
}

- (void)serviceExtensionTimeWillExpire {
    // Called just before the extension will be terminated by the system.
    // Use this as an opportunity to deliver your "best attempt" at modified content, otherwise the original push payload will be used.
    self.contentHandler(self.bestAttemptContent);
}

@end

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>NSExtension</key>
	<dict>
		<key>NSExtensionPointIdentifier</key>
		<string>com.apple.usernotifications.service</string>
		<key>NSExtensionPrincipalClass</key>
		<string>CTNotificationServiceExtension</string>
	</dict>
	<key>CleverTapAccountID</key>
	<string>$(CT_ACCOUNT_ID)</string>
	<key>CleverTapRegion</key>
	<string>sg1</string>
	<key>CleverTapToken</key>
	<string>$(CT_TOKEN)</string>
</dict>
</plist>

#import <UIKit/UIKit.h>
#import <CTNotificationContent/CTNotificationContent.h>

@interface NotificationViewController : CTNotificationViewController

@end

#import "NotificationViewController.h"
#import <UserNotifications/UserNotifications.h>
#import <UserNotificationsUI/UserNotificationsUI.h>

@interface NotificationViewController () <UNNotificationContentExtension>

@property IBOutlet UILabel *label;

@end

@implementation NotificationViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any required interface initialization here.
}

- (void)didReceiveNotification:(UNNotification *)notification {
    self.label.text = notification.request.content.body;
    #if DEBUG
        NSLog(@"did receive notification: %@", notification.request.content.body);
    #endif
}

// optional: implement to get user event type data
- (void)userDidPerformAction:(NSString *)action withProperties:(NSDictionary *)properties {
    #if DEBUG
        NSLog(@"user did perform action: %@ with props: %@", action , properties);
    #endif
}

// optional: implement to get notification response
- (void)userDidReceiveNotificationResponse:(UNNotificationResponse *)response {
    #if DEBUG
        NSLog(@"user did receive notification response: %@:", response);
    #endif
}

@end

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>Application App Transport Security Settings</key>
	<dict>
		<key>Allow Arbitrary Loads</key>
		<true/>
	</dict>
	<key>NSExtension</key>
	<dict>
		<key>NSExtensionAttributes</key>
		<dict>
			<key>UNNotificationExtensionCategory</key>
			<string>CTNotification</string>
			<key>UNNotificationExtensionUserInteractionEnabled</key>
			<string>1</string>
			<key>UNNotificationExtensionDefaultContentHidden</key>
			<true/>
			<key>UNNotificationExtensionInitialContentSizeRatio</key>
			<real>0.1</real>
			<!-- <key>UNNotificationExtensionInitialContentSizeRatio</key>
			<real>1</real> -->
		</dict>
		<key>NSExtensionMainStoryboard</key>
		<string>MainInterface</string>
		<key>NSExtensionPointIdentifier</key>
		<string>com.apple.usernotifications.content-extension</string>
	</dict>
</dict>
</plist>

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
  [self initializeClevertap];

  #if DEBUG
    NSLog(@"DEBUG: %d", DEBUG);
    [CleverTap setDebugLevel:CleverTapLogDebug];
    #ifdef FB_SONARKIT_ENABLED
      InitializeFlipper(application);
    #endif
  #endif
  
  if(lOptions == nil) {
    lOptions = launchOptions;
  }
  
  RCTBridge *bridge = [[RCTBridge alloc] initWithDelegate:self launchOptions:launchOptions];
  RCTRootView *rootView = [[RCTRootView alloc] initWithBridge:bridge
                                                   moduleName:@"Booky"
                                            initialProperties:nil];

   if (@available(iOS 13.0, *)) {
      rootView.backgroundColor = [UIColor systemBackgroundColor];
  } else {
      rootView.backgroundColor = [UIColor whiteColor];
  }

  self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];
  UIViewController *rootViewController = [UIViewController new];
  rootViewController.view = rootView;
  self.window.rootViewController = rootViewController;
  [self.window makeKeyAndVisible];
  [RNBootSplash initWithStoryboard:@"BootSplash" rootView:rootView];
  if ([FIRApp defaultApp] == nil) {
    [FIRApp configure];
  }
  [[UNUserNotificationCenter currentNotificationCenter] setDelegate:self];

  return YES;
}
...
- (void) initializeClevertap {
  [CleverTap autoIntegrate]; // integrate CleverTap SDK using the autoIntegrate option
  [self registerPush]; // register for APN
  [[CleverTapReactManager sharedInstance] applicationDidLaunchWithOptions:lOptions];
}
...
- (void)registerPush {    
    UNUserNotificationCenter *center = [UNUserNotificationCenter currentNotificationCenter];

    UNNotificationAction *action1 = [UNNotificationAction actionWithIdentifier:@"action_1" title:@"Back" options:UNNotificationActionOptionNone];
    UNNotificationAction *action2 = [UNNotificationAction actionWithIdentifier:@"action_2" title:@"Next" options:UNNotificationActionOptionNone];
    UNNotificationAction *action3 = [UNNotificationAction actionWithIdentifier:@"action_3" title:@"View In App" options:UNNotificationActionOptionNone];
    UNNotificationCategory *cat = [UNNotificationCategory categoryWithIdentifier:@"CTNotification" actions:@[action1, action2, action3] intentIdentifiers:@[] options:UNNotificationCategoryOptionNone];
    [center setNotificationCategories:[NSSet setWithObjects:cat, nil]];
    
    [center requestAuthorizationWithOptions:(UNAuthorizationOptionSound | UNAuthorizationOptionAlert | UNAuthorizationOptionBadge) completionHandler:^(BOOL granted, NSError * _Nullable error){
        if( !error ){
            dispatch_async(dispatch_get_main_queue(), ^(void) {
                [[UIApplication sharedApplication] registerForRemoteNotifications];
            });
        }
    }];
}
...
/** For iOS 10 and above - Foreground, NOTE: Also works for iOS 8 **/
- (void)userNotificationCenter:(UNUserNotificationCenter *)center willPresentNotification:(UNNotification *)notification withCompletionHandler:(void (^)(UNNotificationPresentationOptions))completionHandler{    
    /**
      Use this method to perform the tasks associated with your app's custom actions. When the user responds to a notification, the system calls this method with the results. You use this method to perform the task associated with that action, if at all. At the end of your implementation, you must call the completionHandler block to let the system know that you are done processing the notification.
      
      You specify your app's notification types and custom actions using UNNotificationCategory and UNNotificationAction objects.
      You create these objects at initialization time and register them with the user notification center. Even if you register custom actions, the action in the response parameter might indicate that the user dismissed the notification without performing any of your actions.
      
      If you do not implement this method, your app never responds to custom actions.
      
      see https://developer.apple.com/reference/usernotifications/unusernotificationcenterdelegate/1649501-usernotificationcenter?language=objc
      **/

    NSLog(@"%@: will present notification: %@", self.description, notification.request.content.userInfo);

    /** NOTE: As of CT SDK Version 5.2.1, this triggers Push Impressions / Impressions on Campaign Stat page, not Notification Viewed as indicated by name! **/

    [[CleverTap sharedInstance] recordNotificationViewedEventWithData:notification.request.content.userInfo];

    // if you wish CleverTap to record the notification open and fire any deep links contained in the payload, NOTE: This triggers Notification Clicked automatically
    // [[CleverTap sharedInstance]handleNotificationWithData:notification.request.content.userInfo openDeepLinksInForeground: NO];
    completionHandler(UNAuthorizationOptionSound | UNAuthorizationOptionAlert | UNAuthorizationOptionBadge);
}
...
/** NOTE: This is the only one triggered in testing the happy path, other than willPresentNotification **/
- (void) application:(UIApplication *)application didRegisterForRemoteNotificationsWithDeviceToken:(NSData *)deviceToken{
  #if DEBUG
    NSLog(@"%@: registered for remote notifications: %@", self.description, deviceToken.description);
  #endif
}

- (void)didReceiveNotificationResponse:(UNNotificationResponse *)response
                     completionHandler:(void (^)(UNNotificationContentExtensionResponseOption))completion {
    UNNotificationContentExtensionResponseOption actionResponseOption = [self.contentViewController handleAction:response.actionIdentifier];
    completion(actionResponseOption);
}

- (UNNotificationContentExtensionResponseOption)handleAction:(NSString *)action
{
   // If can open some API, to handle custom action
}

Compiling Pods/CTNotificationContent » CTNotificationViewController.m

❌  (ios/Pods/CTNotificationContent/CTNotificationContent/CTNotificationViewController.m:5:9)

  3 | #import <UserNotifications/UserNotifications.h>
  4 | #import <UserNotificationsUI/UserNotificationsUI.h>
> 5 | #import <CTNotificationContent/CTNotificationContent-Swift.h>
    |         ^ 'CTNotificationContent/CTNotificationContent-Swift.h' file not found
  6 | 
  7 | typedef NS_ENUM(NSInteger, CTNotificationContentType) {
  8 |     CTNotificationContentTypeContentSlider = 0,

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\f0\fs42 \cf2 \cb3 * thread #1, queue = 'com.apple.main-thread', stop reason = Fatal error: Unexpectedly found nil while implicitly unwrapping an Optional value
\f1\b \

\f0\b0     frame #0: 0x00000001853a6ebc libswiftCore.dylib`_swift_runtime_on_report
\f1\b \

\f0\b0     frame #1: 0x000000018542da70 libswiftCore.dylib`_swift_stdlib_reportFatalErrorInFile + 204
\f1\b \

\f0\b0     frame #2: 0x00000001850eccb4 libswiftCore.dylib`closure #1 (Swift.UnsafeBufferPointer<Swift.UInt8>) -> () in closure #1 (Swift.UnsafeBufferPointer<Swift.UInt8>) -> () in closure #1 (Swift.UnsafeBufferPointer<Swift.UInt8>) -> () in Swift._assertionFailure(_: Swift.StaticString, _: Swift.StaticString, file: Swift.StaticString, line: Swift.UInt, flags: Swift.UInt32) -> Swift.Never + 356
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\f0\b0     frame #3: 0x00000001850eca1c libswiftCore.dylib`closure #1 (Swift.UnsafeBufferPointer<Swift.UInt8>) -> () in closure #1 (Swift.UnsafeBufferPointer<Swift.UInt8>) -> () in Swift._assertionFailure(_: Swift.StaticString, _: Swift.StaticString, file: Swift.StaticString, line: Swift.UInt, flags: Swift.UInt32) -> Swift.Never + 192
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\f1\b \

\f0\b0   * frame #5: 0x00000001007dbc1c CTNotificationContent`CTContentSliderController.moveSlider(direction=1, self=0x000000012486ba00) at CTContentSliderController.swift:210:9
\f1\b \

\f0\b0     frame #6: 0x00000001007db3b8 CTNotificationContent`CTContentSliderController.showNext(self=0x000000012486ba00) at CTContentSliderController.swift:182:9
\f1\b \

\f0\b0     frame #7: 0x00000001007db3e8 CTNotificationContent`@objc CTContentSliderController.showNext() at <compiler-generated>:0
\f1\b \

\f0\b0     frame #8: 0x0000000182048e58 Foundation`__NSFireTimer + 64
\f1\b \

\f0\b0     frame #9: 0x00000001809afc58 CoreFoundation`__CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 28
\f1\b \

\f0\b0     frame #10: 0x00000001809394e8 CoreFoundation`__CFRunLoopDoTimer + 1008
\f1\b \

\f0\b0     frame #11: 0x00000001809340a0 CoreFoundation`__CFRunLoopDoTimers + 316
\f1\b \

\f0\b0     frame #12: 0x0000000180913d94 CoreFoundation`__CFRunLoopRun + 1964
\f1\b \

\f0\b0     frame #13: 0x0000000180926c30 CoreFoundation`CFRunLoopRunSpecific + 572
\f1\b \

\f0\b0     frame #14: 0x00000001a1341988 GraphicsServices`GSEventRunModal + 160
\f1\b \

\f0\b0     frame #15: 0x0000000183121c50 UIKitCore`-[UIApplication _run] + 1080
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\f0\b0     frame #16: 0x0000000182ebb3d0 UIKitCore`UIApplicationMain + 336
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