post https://partner-api.getpliant.com/api/transactions/custom-fields
Create a new custom field for the organization. Custom fields can be used to store additional information on transactions. For example, you can create a custom field to store an internal identifier, a project name, or accounting related data. Custom fields can be of type TEXT or SELECT. TEXT custom fields can store any text value. SELECT custom fields can store a fixed set of options. Each new custom field is created ACTIVE.