HomeKit expects an application/pairing+tlv8 content type for responses from /pairings, and fails to add the accessory if it gets something different.
You can reproduce the error by attempting to add an accessory as a user who is an admin but not the owner of the home. This will result in a flow that will attempt to use the AddPairing method. On all my devices this fails unless the content type is application/pairing+tlv8.
HomeKit expects an application/pairing+tlv8 content type for responses from /pairings, and fails to add the accessory if it gets something different.
You can reproduce the error by attempting to add an accessory as a user who is an admin but not the owner of the home. This will result in a flow that will attempt to use the AddPairing method. On all my devices this fails unless the content type is application/pairing+tlv8.