Integration Broker - Getting Error "An object of class Compound failed to deserialize. (2,693) An e

In Integration Broker, while attempting to invoke a third-party REST API, I encountered the following error:

"An object of class Compound failed to deserialize. (2,693) An error occurred while trying to unpack the value of an object of the given class."

The error occurs on either:

&DOC = &MSG.GetDocument() 

or

&COM.GetPropertyByName("YEAR").value = 2024;

Below is the relevant portion of the PeopleCode:

Local Document &DOC;

Local Compound &COM;


&MSG = CreateMessage(Operation.xxx_POST);

&DOC = &MSG.GetDocument();

&COM = &DOC.DocumentElement;

&COM.GetPropertyByName("YEAR").value = 2024;

&COM.GetPropertyByName("MONTH").value = 9;