Trying to catch exceptions with metatransactions and defender relay

Hi, following the example for metatransactions with the defender relay posted at, over the sokol network I can sign my name with NAME=Gabo npm run sign and run npm run relay perfectly, however, by signing my name again and sending it, I would expect to be able to catch the error thrown by the Registry.sol contract in the register function: require (owners [name] == address (0), "Name taken "); but I see that apparently, the call through the relay, returned a correct transaction. I have two questions to this scenario:

  1. Why is the exception not thrown?
  2. What would be the best way to capture it?

Thank you in advance for your help