How to get the TestFlight invitation code?

TestFlight is a platform that allows App Developers to make beta versions of their Apps available for testing by their customers. You will need to receive an invitation from the respective App Developer to test their beta releases.

Some Developers have a signup page on their website. If you are unable to find a signup page, you'll need to contact the App Developer directly:

How to contact an app developer - Apple Support

Not all Developers make beta versions of their Apps available for general testing.

See the answer provided by our colleague Ikrupp in this similar thread:--> how to get a invitation code from Apple T… - Apple Community

Thanks and regards

Giulio