smart48.de has an AAAA (IPv6) record (2a03:b0c0:0:1010::1aa:d001) but a test request to this address over port 80 did not succeed. Let's Encrypt will prefer to use AAAA records, if present, and will not fall back to IPv4 records. You should either ensure that validation requests to this domain succeed over IPv6, or remove its AAAA record.
Get http://smart48.de/.well-known/acme-challenge/letsdebug-test: dial tcp [2a03:b0c0:0:1010::1aa:d001]:80: connect: connection refused
Trace:
@0ms: Making a request to http://smart48.de/.well-known/acme-challenge/letsdebug-test (using initial IP 2a03:b0c0:0:1010::1aa:d001)
@0ms: Dialing 2a03:b0c0:0:1010::1aa:d001
@82ms: Experienced error: dial tcp [2a03:b0c0:0:1010::1aa:d001]:80: connect: connection refused
smart48.de has an A (IPv4) record (37.139.22.56) but a request to this address over port 80 did not succeed.
Get http://smart48.de/.well-known/acme-challenge/letsdebug-test: dial tcp 37.139.22.56:80: connect: connection refused
Trace:
@0ms: Making a request to http://smart48.de/.well-known/acme-challenge/letsdebug-test (using initial IP 37.139.22.56)
@0ms: Dialing 37.139.22.56
@100ms: Experienced error: dial tcp 37.139.22.56:80: connect: connection refused
A test authorization for smart48.de to the Let's Encrypt staging service has revealed issues that may prevent any certificate for this domain being issued.
Fetching http://smart48.de/.well-known/acme-challenge/mJgY4VxZQdgh7eqAKd1vVd352QDR-JzxwMBuQtFpsz0: Connection refused