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Before you can use the function, there are 2 preconditions:
The feature “Multiple Instalment Payment Transactions” must be turned on. Please reach out to our support team for more details.
The permission
Update Payment Transactions
must be set for your user role.
This feature is exclusively accessible for unpaid installments. Once the installment has been paid, the option to "Mark as Paid" will no longer be visible.
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