I am starting a new iOS project for a third party and need to use their specified bundle ID as it also links with a third party API that will likely check the bundleID. I don’t currently have access to their developer account. I am worried that if I start the project and use my dev account so I can run it on my device, will this stop them registering the bundleID under their account?
Do unique bundle ID’s only come into affect when adding as an app on AppStore Connect? Will it be fine whilst using a development build or should I try with a different one?
Not if you don’t register it. Just don’t start selling it on your own account.
Yes.