I want to tighten the Sales workflow in ERPNext so that no user can pick, deliver, or invoice more items than what was originally confirmed on a Sales Order. The rule has to fire automatically on three documents—Pick List, Delivery Note, and Sales Invoice—whenever a line item’s cumulative quantity tries to exceed the balance available on its linked Sales Order. Because the work sits squarely inside the Sales module, I expect the logic to run whether a user is in Stock or Invoicing screens, but the validation itself should live with the Sales layer so it stays consistent across the whole cycle. Custom feedback is essential. Instead of the generic “Quantity exceeds reserved” warning, I need friendly, specific messages that clearly reference the item code and the remaining allowable quantity. You can propose message wording or follow the template I’ll share once we start. Deliverables • A server-side script (Python) or client script (JavaScript) that plugs cleanly into ERPNext’s hooks without core edits • Clear instructions on where to place the code and how to migrate it between environments • A brief test plan that shows the validation preventing over-picking, over-delivery, and over-invoicing while allowing valid quantities to proceed I’ll provide access to a staging instance for verification and will sign off once all three documents respect the Sales Order limits and show the new messages.