Updates the lines of an existing buyer invoice identified by the specified invoiceId and line id.
Only the fields provided in the request body will be updated; all other line properties remain unchanged.
This endpoint supports partial updates and can be used to modify details such as unit price, quantity, discount,
taxes, shipping, handling and custom fields. Updates are only made if all data provided is valid.
The following examples will show each property that can be updated. You can update any combination of these examples separately or together.

General validations include:

• Valid buyer invoice id must be provided
• Invoice must be editable (i.e. invoice can not be in complete status, cancelled status or in an automated workflow step)
• Invoice line id in payload must not be duplicated
• Invoice line id must belong to the invoice

This api provides two different request options. The line to modify can be identified either by line number or by the line id.
The guidelines below further define how to use these options.

Line Identification and Validation:

• Line must be identified by either lineId or lineNumber but not both
• Line id must be unique across all lines in the invoice
• Line number must be unique across all lines in the invoice
• Line number must be between 1 and 999