Do you have SSL turned in the admin console?
Are you using a custom SSL certificate?
I'm not sure about SSL, Do you think I need to buy SSL or How should I activate
You need to buy one if you want to make your connection secure. If you don't care about it then you don't.
You generate the certificate signing request from FMS and then import the certificate in FMS once you have it issued to you. There is some good info available, just google "filemaker server ssl"