Hi Denis,
I tried to call the REST API for that entrypoint and it went well:

What I did in Service Studio was add a Rest Service for the entrypoint you mentioned, test it and choose the option Copy to Response Body before Finish (and of course then call the service from a timer or button on a screen to test):
I'm using Service Studio 11.10.0 but I doubt it is because of the Service Studio version that it is not working on your side.
May it be that you have called this web service so many times that they blocked calls from your OutSystems infrastructure IP (hence the error message)?
Regards,
João