RTMS consumption is intended to draw from the Developer Pack credit balance on the RTMS-enabled developer account. That is 0.01 credit per minute without transcription and 0.02 per minute when transcription is enabled. Audio plus diarized transcript uses the 0.02 transcript-enabled rate, not 0.03.
Participant can be on the basic plan but the account must be verified. Invite the account, join, and make the PATCH call to test.
Recall.ai is a Zoom RTMS Preferred Partner and offers further RTMS integration support.