From the Apple Connect API documentation, it seems like Apple does not provide an endpoint to add devices to provisioning profiles (or update profiles in any way, for that matter). Am I missing something in the docs or is this a known limitation?
I got a response from Apple Support, they confirm that indeed there is no such API method. Here's the relevant part of their response for posterity and clarity:
You are correct that the App Store Connect API doesn't provide a direct method to add a device to an existing provisioning profile. To include a new device, you need to create a new provisioning profile that incorporates the desired devices. This process involves deleting the existing profile and generating a new one with the updated device list.