Hi All,
I got the same issue and below is the solution which worked for me.
Added "&scenarioId=FIORI_APPROVE_REQUESTS" to the link which you are executing; Basically, Generic Call App needs to know which scenario it needs to execute.
https://<hostname>.<domain><port>/sap/bc/ui5_ui5/sap/ui5_ca_all_apv/index.html?sap-client=100&scenarioId=FIORI_APPROVE_REQUESTS
Hopefully, this helps!
Thanks
Sri