X_MAIL_CREDENTIAL_MISSING

this deployment configured no mail transport

neither SMTP_URL nor RESEND_API_KEY is set outside development/test, so selectMailDriver installed a driver that refuses. The memory driver used to be installed there instead and reported accepted for mail that never left the process — password resets, receipts and invitations all "sent", none delivered, no error anywhere

set SMTP_URL="smtps://user:pass@host:465" (or RESEND_API_KEY=re_…) and MAIL_FROM="App <no-reply@yourdomain.test>" in the deployment environment, then restart. X_MAIL_DRIVER_UNAVAILABLE is the other half: that one is no driver installed — no mail: in apps/<app>/runtime.ts and no transport variable