Is the TP=Link router unlocked to all networks?
Have you input the giffgaff APN (internet settings) onto the router?
Most device manufacturers now include giffgaff's APN settings in their software updates, for most of their newer devices
This means that simply putting a giffgaff SIM card into a device with the settings will automatically set up the internet and choose giffgaff as the carrier.
Often a simple device restart will fix things.
If this doesn't work, then you will need to manually install the settings
It's not a difficult task and to manually set up these are the settings required for your device
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