Hi @WeT-Klb,
We’ve been investigating this issue as well and found that Let’s Encrypt has recently made some changes to their certificate issuance process, which appear to affect how certificates are generated and renewed—especially when using custom DDNS domains.
The good news is that SSL Certificate version 2.2.63, which is scheduled for release this week, will include a fix that resolves the issue with importing and renewing Let’s Encrypt certificates for custom domains.
In the meantime, if necessary, use the temporary *.myqnapcloud.com certificate for access.