I have a MR6400 router.  I use it whilst on vacation in France with a local French SIM for Internet access.

I have bought a B&You SIM "sans-engagement" with 300Gb data per month.

I have activated the SIM in a mobile phone and tested that it works fine.

It also works to provide a wi-fi hotspot to enble me to access the Internet from other devices.

However...

When I put the SIM in the 4G router the Internet fails to connect.

The router works with a different SIM for another French network and with the UK SIM from my mobile phone - but not with the new SIM.

I have tried everything and not yet solved this problem.

Any ideas/advice gratefully received.