HI,

I got a very similar problem on two different server with different domains since about 1-2 months ago. Which is constant in all error messages is: "500 internal server error". :/

For example (tried acme.sh with new account):

[Sat 26 Mar 11:45:18 CET 2022] _post_url='https://api.buypass.com/acme-v02/new-acct'
[Sat 26 Mar 11:45:18 CET 2022] _WGET='wget -q --content-on-error '
[Sat 26 Mar 11:45:21 CET 2022] wget returns 8, the server returns a 'Bad request' response, lets process the response later.
[Sat 26 Mar 11:45:21 CET 2022] Using sed  -i
[Sat 26 Mar 11:45:21 CET 2022] _ret='0'
[Sat 26 Mar 11:45:21 CET 2022] code='500'
[Sat 26 Mar 11:45:22 CET 2022] Register account Error: {"code":500,"message":"INTERNAL_SERVER_ERROR","details":"HTTP 500 Internal Server Error"}

Older (legacy) certbot:
 

2022-03-26 11:08:43,732:DEBUG:urllib3.connectionpool:https://api.buypass.com:443 "POST /acme-v02/new-order HTTP/1.1" 500 89
2022-03-26 11:08:43,735:DEBUG:acme.client:Received response:
HTTP 500
Content-Length: 89
Content-Type: application/json
Date: Sat, 26 Mar 2022 08:53:50 GMT
Mdc-Correlationid: d0f4e291-cdf5-408a-879f-260ed0f14254
Vary: Accept-Encoding
X-Buypass-Internal-Error-Detail-Code: INTERNAL_SERVER_ERROR
Strict-Transport-Security: max-age=63072000
{"code":500,"message":"INTERNAL_SERVER_ERROR","details":"HTTP 500 Internal Server Error"}
2022-03-26 11:08:43,735:DEBUG:acme.client:Ignoring wrong Content-Type ('application/json') for JSON Error

Sadly not found answers, just similar questions :/
One on my VPS I changed the CA (ACME) server from the BuyPass to a different one and it worked with it. And I got the same problem on my other machine with BuyPass ACME..

Different server, different domain, up to date certbot, certificate renew process (autorenew), with very similar error(s):

2022-03-13 05:03:37,287:DEBUG:urllib3.connectionpool:https://api.buypass.com:443 "POST /acme-v02/authz/[REMOVED]/1 HTTP/1.1" 500 89
2022-03-13 05:03:37,287:DEBUG:acme.client:Received response:
HTTP 500
Content-Length: 89
Content-Type: application/json
Date: Sun, 13 Mar 2022 04:03:35 GMT
Mdc-Correlationid: f3553b6c-6ca7-41bf-87d7-86dc73bc0dc3
Vary: Accept-Encoding
X-Buypass-Internal-Error-Detail-Code: INTERNAL_SERVER_ERROR
Strict-Transport-Security: max-age=63072000
{"code":500,"message":"INTERNAL_SERVER_ERROR","details":"HTTP 500 Internal Server Error"}

I was able to solve this (You can see, it's an older log sample) only one way: replaced the ACME server with a different CA's ACME server, and the certbot worked fine with it (so maybe I'm wrong, but I think the problem is not with my certbot, application).

Yeah, no.

The 500 was fixed, but now everyone just gets this instead:
 

2022-03-31 02:17:55,395:DEBUG:certbot.renewal:Traceback was:
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/acme/client.py", line 156, in answer_challenge
    response = self._post(challb.uri, response)
  File "/usr/lib/python3/dist-packages/acme/client.py", line 96, in _post
    return self.net.post(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/acme/client.py", line 1204, in post
    return self._post_once(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/acme/client.py", line 1218, in _post_once
    response = self._check_response(response, content_type=content_type)
  File "/usr/lib/python3/dist-packages/acme/client.py", line 1073, in _check_response
    raise messages.Error.from_json(jobj)
acme.messages.Error: urn:ietf:params:acme:error:malformed :: The request message was malformed :: Unable to process challenge, authorization is not pending
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/certbot/renewal.py", line 443, in handle_renewal_request
    main.renew_cert(lineage_config, plugins, renewal_candidate)
  File "/usr/lib/python3/dist-packages/certbot/main.py", line 1197, in renew_cert
    renewed_lineage = _get_and_save_cert(le_client, config, lineage=lineage)
  File "/usr/lib/python3/dist-packages/certbot/main.py", line 115, in _get_and_save_cert
    renewal.renew_cert(config, domains, le_client, lineage)
  File "/usr/lib/python3/dist-packages/certbot/renewal.py", line 318, in renew_cert
    new_cert, new_chain, new_key, _ = le_client.obtain_certificate(domains, new_key)
  File "/usr/lib/python3/dist-packages/certbot/client.py", line 334, in obtain_certificate
    orderr = self._get_order_and_authorizations(csr.data, self.config.allow_subset_of_names)
  File "/usr/lib/python3/dist-packages/certbot/client.py", line 370, in _get_order_and_authorizations
    authzr = self.auth_handler.handle_authorizations(orderr, best_effort)
  File "/usr/lib/python3/dist-packages/certbot/auth_handler.py", line 82, in handle_authorizations
    self._respond(aauthzrs, resp, best_effort)
  File "/usr/lib/python3/dist-packages/certbot/auth_handler.py", line 152, in _respond
    self._send_responses(aauthzrs, resp, chall_update)
  File "/usr/lib/python3/dist-packages/certbot/auth_handler.py", line 185, in _send_responses
    self.acme.answer_challenge(achall.challb, resp)
  File "/usr/lib/python3/dist-packages/acme/client.py", line 164, in answer_challenge
    response = self._post(challb.uri, response)
  File "/usr/lib/python3/dist-packages/acme/client.py", line 96, in _post
    return self.net.post(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/acme/client.py", line 1204, in post
    return self._post_once(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/acme/client.py", line 1218, in _post_once
    response = self._check_response(response, content_type=content_type)
  File "/usr/lib/python3/dist-packages/acme/client.py", line 1073, in _check_response
    raise messages.Error.from_json(jobj)
acme.messages.Error: urn:ietf:params:acme:error:malformed :: The request message was malformed :: Unable to process challenge, authorization is not pending

I realize this is a free ACME end-point, and I should be keeping my expectations low, I'm not mad, just... disappointed. 

And it's not an issue restricted to a few hosts, but pretty much ALL the hosts I have ever used BuyPass on exhibit the same issue. This is across multiple data-centers, multiple IP ranges etc.

Also, in case you're wondering why your community participation is low, it's because:

• you don't allow free e-mail domains, because apparently Captcha is hard, so I had to use a work e-mail to get on here
• your OAuth is broken, too

...reminder that this is STILL happening.

@Mats

After the bugfix I was able to renew a certificate on a third VPS (and third domain), with a 'legacy' (older) version certbot used the BuyPass ACME server. The error message(s) disappeared.. :) Thanks for the reply and for the help! (and of course, for the free quality certificates!)

Ps: I not tried to generate/renew the certificates on my other affected two VPS since the reported bugfix. I will try it when my current certificates (from other CA) will expire on them. But I hope they will work also.