Cannot connect with client

Hello I am unable to connect to my remote DB due to this error.  What is the meaning, and how to solve it?  Please see attached.

Make sure that the same ObjectDB version is used on both the server side and the client side.

I'm pretty sure they are, since the update of that version was from last year.  How do I find out exact I'm running?

Check that the same jar file is used on both sides.

If it is the same - try to find the full stack trace of the exception in the log file.

IC,  I am using https://www.objectdb.com/download/2.8.6_02 on the server, and when I downloaded https://www.objectdb.com/download/2.8.7, there is something incompatible, so I had to download the https://www.objectdb.com/download/2.8.6_02 for client instead of use the full version.  Problem solved. thx