The mostly likely cause is a returned check from a donor. Jewel will automatically subtract that negative amount when calculating your next remittance check.
Several things could have happened. A returned check from a donor, a deposit entered after your remittance check was written (you would have needed tech support help), a correction made to a donation in a previous month, or voiding a previous remittance check are all possibilities. There should always be a traceable reason for the difference.
If you are sending paper remittance checks, first void the old remittance check. Then go to Accounting / Make Manual Remittance. Click Edit Check, and recreate the check you just voided. Edit the memo to say: "To replace check#1234, July 2027 remittance".
If you send your remittance via ACH, contact tech support for help.
You are trying to write the remittance check in Write Checks. Jewel doesn't allow this to protect the conference funds from accidental (or intentional) misappropriation. Once you have entered all of your deposits for the month, start the month-end closing process and Jewel will write the remittance check for you. On the rare occasion that you need to write a remittance check outside of the regular monthly cycle, see the instructions at Remittance Checks.