Best answer by Ed_Boost
Thanks for getting involved with the forum!
It looks like it's most likely a temporary issue, it's not something we've had reported to us by other customers, so we'd always advise to delete the app, and re-install it.
9 times out of 10 that will work!
If you still can't top up or add a card to your account, it'd be worth getting in touch with us. You can email us at firstname.lastname@example.org, or if you'd prefer, send us a message to our Facebook or Twitter pages: https://www.facebook.com/boostpoweruk/ or https://twitter.com/boostpoweruk.