Allocating payments/refunds for VAT on QuickBooks Online
I am unsure whether this will work without having access to the QuickBooks file directly. Please let me know how you get on.
Within the VAT screen, click on the 'Record payment' button and record the full value of £19k. Ensure that you select the right bank account you paid the VAT from (even though it is only £15k you paid) and the same date the money left your bank account.
Within the banking screen, on the transaction that shows £15k leaving your bank account click into it and select 'Find match'. Open up the date ranges and see if the VAT payment of £19k you have just recorded is shown here. Of course it will show a £4k difference. I am hoping that you will be able to use the 'resolve difference' toggle to post it to VAT suspense.