[Bitrise docs]: 1) upload provisioning profiles via the right code signing asset management option so steps download them to the VM at runtime. 2) upload the signing certificates to the Code Signing tab. 3) connect the Bitrise account to the Apple Developer portal. If a suspect error is code-signing related, the problem is almost certainly one of these three. Generate a signed IPA locally first: if it fails on your machine, it will fail on Bitrise. Enable the Verbose log input in the signing step for the real error.

Context: Every Bitrise build runs on a clean VM with no signing files. Code signing fails unless you uploaded everything.