Prove childcare costs for UC?

Hi all,

I would like to have a question about childcare cost in UC.
What happens if you can’t meet the requirements in the to-do list in universal credit. For example: they request additional prove of childcare cost been paid such as bank statement or transfer showing the payment. But paid in cash . So I don’t have those.

Usually they are fine with the invoice from the childminder but I have messed up the dates so they request more prove of the payment.
any idea what can possibly happen if I can’t prove it ?

Thank you