Moon reader with Calibre library SSL question

I'm trying to have Moon Reader access a calibre library that is signed by a Let's Encrypt certificate. I get a java error "trust anchor not found".

I can access the calibre libary using Firefox on the android phone along with Firefox on a laptop. Moon reader has a problem with the intermediate certificates.

I have installed the two intermediate certificates from Let's Encrypt in the android certificate manager but I still get the error.

https://letsencrypt.org/certificates/

Does anyone know which certificates to install to allow Moon Reader to access my calibre server?

Thanks!
MR7653