To be able to register OData Services from SAP ERP we also had to create a system alias for SAP ERP in SAP Gateway.
In transactionSPRO open the SAP Reference IMG and navigate to: SAP NetWeaverSAP GatewayOData ChannelConfigurationConnection SettingsSAP Gateway to SAP SystemManage SAP System Aliases and click on the Activity
Enter the details for the SAP system alias
To register our service, go to transaction /IWFND/MAINT_SERVICE
In our case, the service is: GBAPP_POAPPROVAL
In the transaction /IWFND/MAINT_SERVICE, click “Add Service”
Choose the system alias, and register the service.
S6. Assign Role
In the Fiori Apps Library, check the name of the authorization role for the App