In case you face Input validation error during the creation of your labels it means that your GLS account hasn't been activated yet for WebService use.
You can request its activation at the following email address:
Please note that this is valid except for Countries with a direct GLS connection: Italy, Spain, GLS EE (Hungary, Slovakia, Czech, Romania, Slovenia, Croatia), France.
For which you can find a specific guides in our Carrier's Help section.