Own certificate - upload problem

[archos]

Hi, could someone knowledgeable help me how to upload a purchased SSL certificate to Cloudroun. In the instructions it says, Disable Let's Encrypt integration, but I can't find this for the domain.
The certificate is two files and a key
1 Intermediate_CA_chain.cer
2 searxng.cz.cer
3 searxng.cz.key
I tried renaming them differently .pem .txt, but when uploading to Cloudron, it always shows the error Certificate is not valid for this domain. Expecting test.searxng.cz.
Does anyone please know how to proceed to upload the certificate correctly?
Thank you very much for all your advice.