Collabora Online: cURL error 60: SSL certificate problem?

Question

Digital certificates

When integrating Nextcloud with Collabora Online, it gives an error

Please ask your administrator to add ca-chain.cert.pem to the ca-bundle.crt, for example "cat /etc/loolwsd/ca-chain.cert.pem >> /resources/config/ca-bundle.crt" . The exact error message was: cURL error 60: SSL certificate problem: self signed certificate in certificate chain

I am sure that my bundle is configured correctly, as it works correctly with a different domain.
Here is the config for keys
SSLCertificateFile /etc/apache2/ssl/mycert.cer
SSLCertificateChainFile /etc/apache2/ssl/mycert.ca-bundle
SSLCertificateKeyFile /etc/apache2/ssl/mycert.key
Who has already tried installing Nextcloud with Collabora Online? Did it work for you?