Final answer:
The message mentioned, where a company contacts a supplier about missing merchandise and requests an invoice adjustment, is called a claim. It is a formal request to address an error in the delivery of goods.
Step-by-step explanation:
The type of business message described in the question, where a company writes to a supplier to request an adjustment due to missing merchandise, is known as a claim.
A claim is a formal request or demand for something that is due or believed to be due. This specific type of claim is addressed to the supplier in an effort to correct an error related to invoicing and the delivery of goods.