1984hosting ACME plugin not working (outdated + more?)

[iGadget]

For my internal PVE nodes I want to get ACME working. Since I'm behind a NAT firewall and the single IP's port 80 is not available, I'm trying with the DNS API challenge.
Unfortunately, my own web hoster does not provide a DNS API, so I forwarded a subdomain to 1984.hosting, which has a built-in ACME plugin in PVE.
The current version of this plugin shipping with PVE however does not work - it errors out with a 'login failed' message.

As per this Github comment - it seems the 1984hosting ACME plugin shipping with PVE is not working anymore since the file /usr/share/proxmox-acme/dnsapi/dns_1984hosting.sh is outdated.
I manually replaced every management.1984hosting.com entry in that file into 1984.hosting and then it works again - at least up to the point where the DNS challenge TXT entry is created at 1984.hosting.

I would like to report this to the Proxmox Bugzilla, but I'm not sure which component I should connect it to - perhaps 'Backend'?

(Everything described below might be a different issue)

---

However, even after fixing the above issue, I'm still unable get a certificate for my PVE nodes (actual domain replaced by 'my-redacted-domain'):

Loading ACME account details
Placing ACME order
Order URL: https://acme-staging-v02.api.letsencrypt.org/acme/order/66542803/3857977533

Getting authorization details from 'https://acme-staging-v02.api.letsencrypt.org/acme/authz-v3/3485842723'
The validation for my-redacted-domain is pending!
[Tue Aug 30 20:39:32 CEST 2022] Add TXT record using 1984Hosting
[Tue Aug 30 20:39:35 CEST 2022] Added acme challenge TXT record for _acme-challenge.my-redacted-domain at 1984Hosting
Add TXT record: _acme-challenge.my-redacted-domain
Sleeping 30 seconds to wait for TXT record propagation
Triggering validation
Sleeping for 5 seconds
[Tue Aug 30 20:40:11 CEST 2022] Delete TXT record using 1984Hosting
[Tue Aug 30 20:40:15 CEST 2022] Deleted acme challenge TXT record for _acme-challenge.my-redacted-domain at 1984Hosting
Remove TXT record: _acme-challenge.my-redacted-domain
TASK ERROR: validating challenge 'https://acme-staging-v02.api.letsencrypt.org/acme/authz-v3/3485842723' failed - status: invalid

Now I have no clue what's going wrong here. Things I checked already:

1. Checked actual creation of TXT record at 1984hosting - it's there while the script runs and then gets deleted
2. Resolving of my domain at 1984.hosting works both externally as well as internally
3. Changing the internal DNS entry of my PVE host from the internal IP to the external IP makes no difference

What else can I do to debug this issue?