@JPP-1 

I solved this problem by enabling data roaming. To do this, connect to the router then go to tplinkmodem.net and log in - this give you a lot more options than the tp link app. 

Go to network > internet then enable roaming. 

Solved my issue when in Spain using a British sim

I learnt this via the manual, there seems to be very little other information online. 

@nibheis 

There is a trick. In automatic mode, router is unable to find proper login data.

You have to switch to static and fill your provider login manually.

Then it works.

Copy below, unfortunately in czech.

Karel

That's a pity it's not automatic, like other devices do. Here my settings for a french orange sim:

Mobile Roaming: ON

Apn Type: Static

Apn: orange

username: orange

password: orange

Authentication Type: None

@nibheis I faced the same difficulty here in India as AIRTEL uses "Data Roaming" and shows an "R" when you are within India (but not in your home state).

Strangely the other network JIO which also uses "Data Roaming" on Android phones does not show an "R" on the mobile and on the TPLINK MR600 does not need data roaming to be enabled!

Anyways here is the way to enable data roaming - 

1. log into http://tplinkmodem.net/ (ensure both your PC/laptop are connected to the MR600's wifi)

2. Enter your password (no username is required)

3. Click on ADVANCED tab

4. Click on NETWORK tab

5. Click on INTERNET tab

6. Slide DATA ROAMING to the right (ON)

Hope this helps!

Just found out the you have to swtich on roaming but this option is only available in the web interface, not in the app!