@minuri_perera, I first made a check with your xlsform to see if there were any syntax issues. I did not find any. Then I uploaded the same to my account and then made a quick test. Made a submission with Enketo and was able to smoothly submit the data to the server.
What I assume here is that you have either accidentally missed some mandatory variables to fill or you are probably using an outdated browser to collect data (if this is the case try updating your browser or use some modern browsers like Chrome, Edge, Firefox etc.). Ensure these and this should solve your issue.
