So, this was hair pulling. Out of the blue I started to get this error in the middle of migrating 20+ sites. Thought I may have hit the rate limit, and maybe I did hit some internal limit. Logs were not great in wordops.log or perhaps I did not know where to look. I dumped the output of the acme.py where it called acme.sh. Low and behold --
[Mon Jun 14 23:53:54 UTC 2021] Using CA: https://acme.zerossl.com/v2/DV90
[Mon Jun 14 23:53:54 UTC 2021] No EAB credentials found for ZeroSSL, let's get one
[Mon Jun 14 23:53:54 UTC 2021] acme.sh is using ZeroSSL as default CA now.
[Mon Jun 14 23:53:54 UTC 2021] Please update your account with an email address first.
[Mon Jun 14 23:53:54 UTC 2021] acme.sh --register-account -m my@example.com
[Mon Jun 14 23:53:54 UTC 2021] See: https://github.com/acmesh-official/acme.sh/wiki/ZeroSSL.com-CA
[Mon Jun 14 23:53:54 UTC 2021] Please add '--debug' or '--log' to check more details.
[Mon Jun 14 23:53:54 UTC 2021] See: https://github.com/acmesh-official/acme.sh/wiki/How-to-debug-acme.sh
I guess I assumed it was creating an account with the initial email as it was working well. In any case, was able to get by this, by simply registering an account.
acme.sh --register-account -m <your email>