ng serve
http://localhost:4200

{
    "fieldInfo": {
        "firstName" : "Firstname is a required field",
        "middleName": "middleName is not a required field",
        "lastName" : "Lastname is a required field",
        "emailId": "Email is a required field",
        "mobile" : "Mobile is a required field",
        "password" : "Password is a required field"
    }
}

import { Injectable } from '@angular/core';

@Injectable({
  providedIn: 'root'
})

export class ValidationMessageService {
  validationErrorObj = [];
  public getValidationMsg(validationId: string): string {
    return this.validationErrorObj[validationId];
  }
}

validationErrorMsg() {
  this.apiService.getFieldInfoMessage().then(
    (res) => {
      if (this.validErrorMsgService.validationErrorObj.length === 0) {
        this.fieldInfoMsgArr = res['fieldInfo'];
        console.log('Field Info Array => ', this.fieldInfoMsgArr);
        this.isLoading = false;
      }
    }, (error) => {
      console.log(error);
      this.isLoading = false;
    });
  }