If you're trying to refresh the bank connection and it's not working, or if the balance shown is incorrect, please follow this guide.
Unlink all your children's accounts by clicking on the red trash can next to the linked account. You can find this at Settings > Bank accounts. See video below for this step.
Go back in to the Bank accounts page. There is now another red trash can button at the bottom of the page. Click on that. See picture and video below for this step.
Make sure you close the app completely before you start setting things up again. So don't just leave the app, but actually close it.
Start the pairing process again!
It is important to know that this fix will remove the child's goal, it will instead be converted to a wish. They can of course create the same goal again.
Video for the first two steps.