I have an individual apple developer account. I bought it mainly so I could use a few of the advanced APIs (e.g. NetworkExtensions) in an app that I’m testing/developing. There’s another programmer with whom I collaborate. I want him to also have access to the app so I assigned him the “App Manager” role in iTunes Connect. However, I’m unsure about what he has to do afterwards so that he can work on the same app as me. Can he directly fork the project and access the APIs? Does he need certificates?
iTunes Connect is a separate service from the Apple Developer portal. Development privileges are not assigned via iTunes Connect.
Additionally, since you are using an individual developer account, there is no way to grant another registered Apple Developer access to your team. That functionality is only available to Organisation account.
The problem can be solved in part by granting your colleague access to your code repository. That way you both can collaborate over code. If you want him to test the app on device, you can choose to export your identity on to his machine (Recommended only if you trust him with this thing).