@Tony thanks, after another 12 hours faffing about I discovered the same answer through trial & error. Supplier is claiming it's my error and will not accept return. Even though the description was...

Set up first time network last week with 2x AC1300 plus two RE300 plug in extenders. Which work OK, not great. So now I have 3 more RE300 extenders to add to the network but have tried everything and...