The send payments input box has a pretty bad UX flaw. The example input value is 00.00, but as you start entering numbers the decimals disappear. Nearly every time I use it I end up entering 1000 when I mean 10.00.
The UI is particularly misleading here, but based on all other banking apps I would expect to need to fill the decimals. The least dangerous approach would be to require the decimals to be filled in - worst case you 1/100 of what you wanted to send, rather than 100x.
This also seems to be a fairly long standing issue: