Hi Mohamed,
I think you are using https://sapes1.sapdevcenter.com/sap/opu/odata/IWFND/RMTSAMPLEFLIGHT/ as your backend endpoint URL. The problem might be that you haven't configured your HCPms trial account to access this service via HTTPS.
Please check the following blog
How To use HTTPS connections with SMP Cloud
Can you also describe what happens when you click on "Ping" to your backend?
Best regards
Claudia