The online deposit will only appear on the cash register from the date of the appointment for which the deposit was paid.
If you open the bill on the cash register before the appointment date, you will not see the deposit.
As long as the bill remains open on the cash register, the deposit cannot synchronize correctly.

Did you open the bill beforehand?
Then you need to remove it from the "open bills" column.
You can find the "remove" button at the bottom left of the bill.

(If you don’t see this option, you don’t have the user rights to delete it.)