Set an invoice customer or asset

When to use this endpoint

Use this to correct the billed target without recreating the invoice.

The request must use a logged-in CRM session or valid signed API credentials and is scoped to that tenant.

Users whose legacy crm_access mask contains bit 64 receive {"error":"no permission to access api"}. No record-owner check is made.

Parameter	Type	Required	Description
`id`	Positive integer	Yes	Active invoice ID.
`customer_id`	Positive integer	Yes	Customer or asset ID.
`customer_type`	Integer	No	Defaults to `0` for customer. Type `1` stores the asset as target and resolves its owner as the invoice customer.

$result = FM_api('Invoice_setCustomer', ['id' => 981, 'customer_id' => 1042, 'customer_type' => 0]);

{
  "ok": 1
}

Response	Condition
`{"error":"not logged in"}`	No authenticated tenant context is available. Invalid signed credentials can be rejected by the dispatcher before the handler runs.
`{"error":"cannot edit invoices that are marked Paid"}`	The invoice status is 2.
`{"error":"invoice does not exist"}`	The invoice is absent or deleted.

Legacy application errors may be returned with HTTP 200. Check the decoded response for error, not only the HTTP status.

An asset without an owner is stored with customer ID 0 while retaining the asset target. The handler does not independently verify customer/asset existence.
An unchanged resolved target returns success with warning: no change necessary.

Rebuilds customer_details at the invoice date, marks the resolved customer as having invoices, advances last_edited, and fires Invoice_edit.

The main invoice editor and customer-type enforcement widget call this route.

The QuickBooks connection widget can use this route to correct an invoice target.