I'm trying to port out my number, but keeps getting service address error

Sue, the process for porting is very specific and is monitored by the FCC. We follow the policies to the letter to make sure we are in compliance.
If something doesn't match up, it will be rejected.
I would encourage you to review this article and work with your winning carrier to address the issues you're experiencing.
https://support.ringcentral.com/porting.html