Email Sending - unauthorized sender for apple private relay

[eternal garnet]

Anyone else getting Permanent Unknown error: permanent error (550): 5.1.1 <[email protected]>: unauthorized sender when sending to Apple Private Relay (possibly other providers as well)?

Note: sending from subdomain, not root. The subdomain is onboarded on Email Sending.

Also, seems that the dmarc record isn't locked, even though it says so in Email Sending settings