Trust anchor for certification path not found

i build a fdroid repo. When I use the app to connect to this repo, the following error occurs.
Has anyone encountered the same problem and how to solve it?

config.yml ? setup? nginx? how? Exact error?

This error occurs when adding a new software library to the fdroid application.

Ubuntu 22.04.3 LTS

Error message : Trust anchor for certification path not found.

Could you provide more of the transcript where that error appears? It doesn’t ring any bells for me.

Very little information, but it should be some certificate missing on the server or not being included in the tls handshake, no?