Indeed. We’ve created a ticket to fix the notice, write a better custom domain documentation & improve the error we received from our ACM to ease future investigation. I’ve pushed to productboard the fact that users may want to upload their own certificate for this “specific” wildcard certificate usage.
To me, 1. seems the best option, since our ACM will automatically renew the certificate 1 month before expiration. 2. would require you to provide us the wildcard certificate manually, way before it expires to avoid service interruption.
Let me know if that helps 