Lets Encrypt Request Certificate broken in centos7

My Virtualmin Server is behind a Pfsense Firewall using 1:1Nat. DNS, etc. working fine. These Ports are open: 993, 25, 465, 443, 80, 110, 143, 995, 587

I can put a test.txt file into /home/my.domain.com/public_html/.well-known/acme-challenge/test.txt and open from externally it by using the proper my.domain.com.

I get:

Parsing account key... Parsing CSR... Registering account... Already registered! Verifying www.domain.com... Traceback (most recent call last): File "/usr/libexec/webmin/webmin/acme_tiny.py", line 203, in main(sys.argv[1:]) File "/usr/libexec/webmin/webmin/acme_tiny.py", line 199, in main signed_crt = get_crt(args.account_key, args.csr, args.acme_dir, log=LOGGER, CA=args.ca) File "/usr/libexec/webmin/webmin/acme_tiny.py", line 128, in get_crt wellknown_path, wellknown_url)) ValueError: Wrote file to /home/my.domain.com/public_html/.well-known/acme-challenge/nEY4exEhE5xVet5cXVnedawMbdI3YPhlnpjIZgRS_Sw, but couldn't download http://my.domain.com/.well-known/acme-challenge/nEY4exEhE5xVet5cXVnedawM...

There are no relevant logs in /var/log/messages No .htaccess file in public

I can not observe file creation in the acme-challenge subfolder though.