@yashpathan 

Hi, thanks for posting here.

Can you share the screenshot of the error message? Did you test 2 routers using the same SIM card? And what is the hardware and firmware version of your TL-MR6400.

There could be several reasons why you are not able to access the internet or receive a signal with your 4G LTE router. Here are a few troubleshooting steps you can try:

    1. Check your SIM card and network coverage: Ensure that your SIM card works fine on other 4G devices and you are within the coverage area of your mobile service provider. Weak signal reception can result in poor internet connection or no connection at all.

    2. Make sure your SIM card has been detected by the 4G LTE Router and not locked by PIN code. You could check SIM Card Status on Advanced->Status page to confirm it:

       If it shows "No SIM card detected", follow this guide for troubleshooting。

       If it shows "PIN Required", go to Advanced->Network->PIN Management to enter PIN code of your SIM card to unlock it.

    3. Verify APN profile settings: Check if the Access Point Name (APN) settings on Advanced->Network->Internet page are correct. If not, try other available profile or create a new profile manually.

    4. Factory reset the 4G LTE Router, pressing and holding the reset button for about 10 seconds. Keep in mind that this will erase any customized settings, so make sure to note them down before resetting.

    5. If the above suggestions did not resolve the issue, this is a detailed FAQ for more troubleshooting tips.

You might have to contact TP-Link local support if the above suggestions do not resolve the issue.