Just to say I had a similar issue but I followed Endoman’s advice and messaged Avis yesterday. Everything was sorted within 24 hours and they messaged back to say all of my BAH bookings now have my Preferred number attached and indeed, I can see all of them in the Avis app. I appreciate some posters have advised to input the Avis number at the time of booking but for some reason, I couldn’t see the relevant field for these bookings.