The advice is to upgrade.
1. Genero 2.50 was released in Nov 2013 and supported until the release of Genero 3.20 in June 2019 or thereabouts.
2. If using GMA client with GAS, then you are using the runOnServer front-call.
a) The runOnServer front-call was introduced in Genero 3.00 (second entry in Table 5
http://4js.com/online_documentation/fjs-fgl-manual-html/#fgl-topics/fgl_whatsnew_300v.html)
b) The GAS protocol changed between 2.50 and 3.00.
http://4js.com/online_documentation/fjs-gas-manual-html/#gas-topics/c_gas_migrate_300v.htmlYou did not specify the URL but if it was of the form .../ua/r/.../t100app then the 2.50 GAS would not know what to do with it
If you were using a supported version combination, there is no fundamental difference in the GAS configuration and URL for a web application in a browser and using runOnServer to run the same application inside a mobile app.