Website URL type of encoding and how to decode

I saw this type of URL on a hospital appointment webpage:

www.hospitalcompanyname.com/RegistForm.aspx?newx=Jgm02RFjC3oL3hLPTHj8CyBX3onnc50axGlfkiafSRFzUO66UGfIMlWObZ5k72C2iDcoCzYPmy3JZKEdr0up8g==

My question is what type of encoding is this?

I know its not base64 because I tried to decode it using the plethora of base64 websites online and it does not work. I'm curious as to what this encoding is and what it actually says.

Thanks.