Your version of RealVnc is an evaluation version only, once you get a full licensed version the pop up will no longer be an issue.
Where did you get the RealVNC software? Was it bundled with the SCCM plugin module?
We use RealVNC free edition just to get onto historical systems. I don't believe it was bundled, but I am unsure. I had previously installed and then uninstalled RealVNC + as this gave secure authentication and I was testing it in conjunction with another project.