Hi,

I would not worry about it, see the few post below which all had a successful outcome when getting the same message :

https://www.flyertalk.com/forum/brit...id-flight.html (post 15)
https://www.flyertalk.com/forum/brit...n-bio-lhr.html (post 11)
https://www.flyertalk.com/forum/brit...not-valid.html (post 7)

Seems to be an issue which can be resolved at the airport, maybe just get there a little earlier than planned. There are a few more examples I can pull up if it would help calm the nerves. One of the posts mentioned they contacted the twitter team - not sure if you can do this and see what they say, i can only speak positively of the twitter team so hopefully they can alleviate any concerns.