If you attempt to change your mobile phone handset, and keep the same number – a very common operation in 2020 (updated in 2021, and… yes, in 2022, I still find people regularly get a new phone handset) – you may find you have difficultly accessing your Barclays Banking app in your new device.
Still happens in 2025, for your information… I got a new iPhone and found myself once again trapped in this loop. And yes, the phone number needed removing from the account, before it could be added again.