Troubleshooting
Role: Inventory & procurement managers · AccountantsArea: Accounting · Inventory · Serialized Inventory · All versions · All business types
What you're seeing
You're trying to clear or correct an invoice that has a serialized piece of equipment on it — for example, by adding the equipment back at a negative quantity to zero out the cost. When you try, ServiceTitan requires a serial number to add that equipment, but it won't accept the original serial number. Once a serial number has been used on an invoice with its item, the system blocks that same serial from being added to any later transaction, including returns and adjustment invoices.
Why this happens
Reason 1
A serial number can only be used once.
Serialized inventory tracks each unit by a unique serial number across its whole life cycle, so once a serial number is consumed on an invoice, the system won't let you re-enter that exact serial on another transaction. That's what blocks the straightforward negative-quantity correction.
Before you start
You need permission to create adjustment invoices and inventory adjustments. If you don't have it, contact your administrator.
Consider keeping a dedicated non-inventory item in your Pricebook for these cost corrections, rather than reusing a real item.
How to fix it
The original article's method has two parts: create an adjustment invoice to bring the cost down, then create an inventory adjustment to bring the item and its serial number back to Available.
1Create an adjustment invoice to bring the cost down
Find and go to the invoice.
On the invoice screen, click Add an adjustment invoice.
On the adjustment invoice, add a non-inventory equipment/material with the same cost but in a negative quantity. This pushes the job cost down by the matching amount.
✓ Next · With the cost brought down, continue to step 2 to restore the item and its serial number to inventory.
2Create an inventory adjustment to restore the item and serial
On the navigation bar, click Inventory.
In the side menu, click Adjustments.
On the Adjustments screen, click Create New.
On the Create adjustment screen, add the item used on the original invoice.
In the Serial Numbers column, enter the serial number and add a hyphen at the end.
✓ Done · The original article states this brings the item quantity and the serial number back to Available in the warehouse.
Still not working?
Contact ServiceTitan Technical Support at go.servicetitan.com/ask with:
The invoice number and the serialized item/equipment involved
The original serial number and what the system does when you try to re-enter it
Whether your tenant has the Automated Refund Workflow enabled
Which steps from this article you already tried
Want to learn more?
Create, edit, and copy inventory adjustments ›
Full walkthrough of building and managing the inventory adjustments used in step 2.
Edit serial numbers in your pricebook ›
How to view and correct serial numbers on items in your Pricebook.
Get started with serialized inventory ›
Overview of how serialized inventory tracking works and how serials move through their life cycle.