---
title: "Updates an existing fixed-amount billing entry. Only fields listed in the FieldsToUpdate array will be modified. Valid field names: Amount, InventoryItemIDFK, Notes."
method: PUT
path: "/api/FixedAmount"
tags: ["FixedAmount"]
---

# Updates an existing fixed-amount billing entry. Only fields listed in the FieldsToUpdate array will be modified. Valid field names: Amount, InventoryItemIDFK, Notes.

`PUT /api/FixedAmount`

Fixed amounts that have already been invoiced cannot be updated. Remove the linked invoice line first to release the record. TaskIDFK and ProjectIDFK cannot be changed — to move a fixed amount, delete it and create a new one.

## Request body

- UpdateFixedAmount — Payload for updating an existing fixed-amount billing entry. Only fields named in FieldsToUpdate are applied.
  - `FixedAmountID` integer — The ID of the fixed amount to update. Must belong to the authenticated account.
  - `FieldsToUpdate` string[] — Names of the fields to apply from this payload. Valid values: Amount, InventoryItemIDFK, Notes. Fields not named here keep their current values.
  - `Amount` number, double — The fixed billing amount, in the currency of the customer the record's project belongs to. Cannot be cleared.
  - `InventoryItemIDFK` integer — The inventory item used for this fixed amount. Must exist in the account. Cannot be cleared.
  - `Notes` string — Additional notes, maximum 255 characters. Naming Notes in FieldsToUpdate with a null value clears it.

## Response `200`

Returns the updated fixed-amount entry.

- FixedAmountDetails — A fixed-amount billing entry for fixed-price project invoicing, linked to a project, task, and inventory item.
  - `FixedAmountID` integer — Unique identifier for the fixed amount entry.
  - `ProjectIDFK` integer — The project this fixed amount is linked to.
  - `ProjectTitle` string — Title of the associated project.
  - `ProjectCode` string — Short code of the associated project.
  - `TaskIDFK` integer — The task this fixed amount is linked to, if any.
  - `TaskTitle` string — Title of the associated task.
  - `InventoryItemIDFK` integer — The inventory item used for this fixed amount.
  - `InventoryItemName` string — Name of the inventory item.
  - `Amount` number, double — The fixed billing amount.
  - `Notes` string — Additional notes on the fixed amount.
  - `isInvoiced` boolean — Whether this fixed amount has been included on an invoice.
  - `CustomerIDFK` integer — ID of the customer company the fixed amount's project belongs to.
  - `InvoiceLineItemIDFK` integer — The invoice line item this fixed amount is linked to, if it has been invoiced.
  - `InvoiceIDFK` integer — The invoice (Transaction) the linked line item belongs to. Only populated when includeInvoiceDetails=true.
  - `DateCreated` string, date-time — Date the record was created.
  - `DateUpdated` string, date-time — Date the record was last updated.
  - `UpdatedByUserIDFK` integer — User ID of the last person to update this record.

## Other responses

- `401` — Unauthorized

## Changes

- **2026-08-30** `e99843f3c878` — 1 info
  - endpoint added

[Change history](https://skmtc.dev/avaza/apis/avaza-api-documentation/changes/api/FixedAmount/put.md)

---

[API](https://skmtc.dev/avaza/apis/avaza-api-documentation.md) · [All operations](https://skmtc.dev/avaza/apis/avaza-api-documentation/llms.txt) · [OpenAPI document](https://skmtc-service-production.skmtc.workers.dev/v1/apis/avaza/avaza-api-documentation/revisions/e99843f3c878/schema)