Extender is connected to Router and devices are connected to wi-fi - but wont connect to internet

Hi

I'm hoping for some help, because this is driving me mad.

I've have followed all the instructions, and the range extender is located within good reach of the router, and the devices are located in good reach of the extender - all lights are green.

All the devices I attempt to the extender locate the signal which shows as a strong signal on all the devices I have tried. I can easily connect the devices to the wi-fi signal provider by the extender, and it shows as connected (so far I have tried on 2 different Amazon devices, 2 different Samsung phones, as well as a Lenovo laptop.

Regardless of which device I try and regardless as them showing as being connected to the wi-fi with a strong signal, I can't get access to the internet on any of them. They all show their own variation of the same "check your internet connection status" message.

Help??? I'm going insane.

Many thanks

Martyn.