This POST endpoint is used to add UBOs to a subaccount under your organization.
To use this endpoint, you need to provide the required parameters in the request Body, including first_name, last_name, tax_id, and other UBO details.
The endpoint will then return a successful subaccount UBO token for the newly added UBO. The response will contain a JSON object indicating the status of the request and any relevant subaccount UBO details.