Because json-simple is old and deprecated.

Serialize config in multiple "toml-tables".
Example:

[adfly]
enabled = true
userId = 12345
apiKey = exampleKey

And also update configuration using default configuration on update or absence config entries.

Add permission to see the raw link. Maybe something like earny.bypass.* or earny.bypass.google.com

How about replacing links in users messages with a generated url shortener?

Maybe with regex

A timeout option in config and there should be a check each n minutes if the backend server is online.

I think it is the same as the adf.ly api just on another domain, but check this please.
API Docs: https://adult.xyz/static/other/adult_api_v1_documentation.pdf?v=20181220

We want to move the logic of the shorteners to my backend server (unfortuanally closed source). A example GET request is: https://earny.deeprobin.de/short-url/adfocus/?key=f04d83996aa31670727effc25cc41013&url=https%3A%2F%2Fone.one.one.one%2F

For adfly is it /short-url/adfly/?id=USER_ID&key=API_KEY&url=URL
For adult.xyz is it /short-url/adult/?id=USER_ID&key=API_KEY&url=URL

I didn't found API docs, but this repository uses the api.