There are a few possible causes for this.
For carrier issues, it’s always best to start by reaching out to your carrier, since they can access logs and determine the cause of the issue (whether it’s device related or on their end) instantly.
If you’d like to troubleshoot by yourself, there are a few things you can check
- Check if the APN is configured correctly based on your carrier documentation
- Check if the device original IMEI 1 and IMEI 2 are in tact (BraX3 authentic IMEIs start with 35000216)