If you do not clear a negative balance, Checkout.com carries the unresolved negative balance forward to the next reporting period rather than writing it off. It then appears on your statement as a Carry Forward (Remittance Currency) amount, and offsets against future settlements until it's cleared.
You do not receive a settlement payout while your Available balance is negative. Clearing it quickly keeps your settlements running.
To request a breakdown of what makes up a carried forward amount, contact your account manager or request support.