Thank you for your post.
FileMaker Server 16 does not accept intermediate certificates with .p7b file extension. Try using:
... to change the .p7b file to .pem, or get a .pem file from Register.it.
Our Testing department would like to get the current certificate files that were sent to you. I have sent you a private message with instructions where to send the files.
i've canceled the certificate sent and i've requested another certificate with same parameters; a new one has been issued and it works!
Probably the first one contained something wrong. The difference form my side is that in the new request i've indicated OTHER in the type of web server instead of Apache.
Many thanks and regards