Error message "You can execute a test plan only in a Quality system" occurs after executing a test plan in Test Your Processes App of Demo system.
SAP S/4HANA Cloud Demo system
Reproducing the Issue
1. Go to Test Your Processes App.
2. Select a Test Plan and click "Execute" or "Execute with variants".
3. Error message "You can execute a test plan only in a Quality system" occurs.
The function of executing a test plan is not supported in Demo system or Product system.
Execute a test plan in a Quality system.
For more information about Test Automation Tool for S/4HANA Cloud, please refer to the following KBA.
2129147 - Test Automation Tool for S/4HANA Cloud - Additional Info
Test Automation Tool, You can execute a test plan only in a Quality system, Demo system, Quality system, Test Your Processes , KBA , CA-CTT-S4C-TYP , S/4HANA Test Tool FIORI app. Test Your Processes , Problem