Authorizations
Bearer authentication header of the form Bearer <token>, where <token> is your auth token.
Body
application/json
The custom field values to set
Available options: 
alert, billable_metric, charge, commit, contract_credit, contract_product, contract, customer, discount, invoice, product, rate_card, scheduled_charge, subscription Custom fields to be added eg. { "key1": "value1", "key2": "value2" }
Response
200
Success