Hi
What are the dynamic variables you are passing to BDC?
Please add the Exceptions to your RFC, returning the error/warning messages returned from BDC.
Trap them in the ODATA service and return it in response.
You may know what is the error.
Also, make sure that the Fiori login Userid is having the authorization to the tcode - call transaction inside BDC.
REgards,
Venkat