@Mubb 

Good day.

Thank you very much for your time and patience.

For your case, please refer to the following information:

1. Make sure the sim card has been detected;
2. 
3. Check the IP address and the default APN settings;

---if there is no IP address and default APN settings showed none, please manually create a new profile;

Just in case all failed, we might need the following information so that we could forward your case to our senior engineers:

1. If you tried another sim card, would TL-MR100 work properly?
2. Where are you located and how long have you had the router?

Thank you very much.

@Avi1675 

Hi, could you please refer to this link to do some troubleshooting:

[Troubleshooting]No internet service on LTE Gateway Router

if no improvement, you could send an email to support.forum@tp-link.com with the required information for further assistance.

Thank you very much and wait for your reply.