In case of problem, the methods of GWS classes can throw an exception and set the STATUS variable with the appropriate error number.
DEFINE req com.HTTPServiceRequest,
       data STRING
...
LET req = com.WebServiceEngine.getHTTPServiceRequest(5)
...
TRY
   ...
   CALL req.readTextRequest() RETURNING data
   ...
CATCH
   CALL show_err(SFMT("Unexpected HTTP request read exception: %1", STATUS))
END TRY
For some errors, a human-readable description of the error code is available in the SQLCA.SQLERRM register.