It might be for a number of reasons.
You could have reached the £2200 limit for sending money to your other friendz.
Your friend has already reached the £2200 limit for receiving money.
If you'd like specific information for any of these please get in touch with our support gurus (firstname.lastname@example.org). They'll be happy to give you a hand understanding how this works.
Equally, on rare occasions, system trouble could affect the way the app work causing payments to not work. If you see anything like this please notify us immediately so that we can assist.