If you get the error message "A problem occurred communicating with the server" while using the Memory-Map app, it doesn't give you much information about the error or how to solve it.
The first thing to do is check your WiFi or 3G/4G connection. Are you connected to the internet? Open google.com in your browser and see if it works.
If that works, see if you can access https://w2.memory-map.com in your browser. This is the site that hosts the Memory-Map activation services and if the browser can't access this site, then neither will the Memory-Map app.
If the browser can not access https://w2.memory-map.com, then it may be a "root certificate" problem. Some older Android devices may be missing the up to date "root certificate", which is used by many websites for secure communication. Some device may allow you to install a root certificate manually. The root certificate public key, (which is installed on every modern device that uses the web), is attached to this article. You can download this CRT file and copy it onto your device into the Download folder. The way you install the certificate depends on the device manufacturer. One older Samsung we have here in the office, has it under Settings, Personal, Security, Credentials, Install from Device Storage. It found the CRT file automatically, and fixed the problems.
If the browser can access https://w2.memory-map.com, check to see if you have some kind of firewall, or anti-virus security software that is blocking the app from accessing the internet.