Auditing a total customer outstanding field to the sale invoice

Organisation - American Wholesale Distributors Inc

Ticket - https://cin7.zendesk.com/agent/tickets/222049

With the current system, we are unable to get the total customer due amount printed on the invoice. Only the specific invoice due amount can be printed on the invoice. we can show only the specific sale order due amount in the sale invoice. But this customer has requested to see the total customer outstanding amount in the sale invoice view and in the sale invoice template. along with the specific sale invoice due amount.