Hej Gerrit,

I’m sorry to hear that you are having problems with additional devices. Unfortunately, we won’t be able to troubleshoot easyconnect SIMs from T-Mobile as they are not connected to IoT Creators.
T-Mobile should have a support number, which you can call for help or you could reach out to 1nce, since the service is based on their platform.
If you are using SIM cards from IoT Creators, then the APN advice from fm would be your best bet and you can also contact us again with the SIM card details to troubleshoot them on our end, if that hasn’t solved your issues.