We are in the middle of the final brownout for ACMEv1. We will end the brownout on Tuesday, May 25th and there will be one week before we entirely disable ACMEv1 as a viable way to get a Let's Encrypt certificate.
Beginning June 1st, users who attempt issuance with ACMEv1 will be returned this message:
ACMEv1 is deprecated and you can no longer get certificates from this endpoint. Please use the ACMEv2 endpoint, you may need to update your ACME client software to do so.
If you need help updating your client software please look at this thread: