DataSync Agent cannot reach Dell ECS onprem object storage with SSL error

The errors I get are following:

S3 Exception: op=ListObjectsV2 bucket=xyz code=-1 type-99 exception=, msg=curlCode: 60, SSL peer certificate for SSH remote key was not OK

There was a certificate verification error communicating with the object storage endpoint. Verify the ServerCertificate provided for this location is a complete certificate chain for your object storage location.

I uploaded the ECS node chain PEM certificate when creating a Task in DataSync console. Agent is online, it has connectivity to ECS node on IP level - test passes.

Are self signed certificates good for DataSync Agent?

Is there a way to get more detailed info on why the certificate was rejected and by which node/host or service?