I think you have a Palo Alto brand firewall blocking ACME HTTP Challenge requests.
We have seen this a lot over time. See this thread which explains the remedy. It even happens to be someone using Filemaker (although this is not specific to that). Test Validation Works, Cert Request Fails in FileMaker Pro - #4 by MikeMcQ
These two requests demonstrate it:
# Works as expected
curl -i -m5 http://fms.dsc.umich.edu/.well-known/acme-challenge/Test404
HTTP/1.1 404 Not Found
Date: Wed, 04 Feb 2026 20:28:43 GMT
Server: Apache
# Fails with a user-agent string similar to Let's Encrypt servers
curl -i -m5 http://fms.dsc.umich.edu/.well-known/acme-challenge/Test404 -A "Mozilla/5.0 (compatible; Let's Encrypt validation server; +https://www.letsencrypt.org)"
curl: (28) Operation timed out after 5001 milliseconds with 0 bytes received