Problem

mars - ERROR - 20190507.231202 - Request validation failed:
mars - ERROR - 20190507.231202 - restricted access to valid data.
mars - ERROR - 20190507.231202 - For more information, look at 
mars - ERROR - 20190507.231202 - https://confluence.ecmwf.int/display/UDOC/MARS+access+restrictions#valid.

Solution

You are not authorised to access valid data.

Check the MARS access restrictions and modify your request accordingly.