Each user has their own personal code - it is used to identify who is accessing the account.
Ah.
My wife and I use the same code!
It doesn’t really matter, we used the same code for probably 15 years. It was only when we asked for the savings accounts we got the second code.
It’s all a mystery - to me, and it seems to some here! Hopefully I will have an answer tomorrow from Britline.
But when I tried to use the one 6-digit numeric code that we have and which my wife already uses, it appeared that I would have to disable the app on my wife’s phone to use it on my phone.
I’ve used contactless payments on my phone in the UK for over 5 years. But having been in France now for 2 1/2 years and loving France as we do, I’m no longer surprised by things like this 
It’s designed to work that way. One person can use the app on one device. Hence the need for separate codes personnels when the account is used by more than one person
Yes, that’s my point - I need to get my own code.
Do you have you’ve never had one or you just don’t know it?
If you haven’t clicked that link then give it a go and see if it allows you to set one up. My wife forgot hers and used that process and it sent a couple of SMS messages for security and then gave her a new number.