Updates the settings of a customer by its accounting system ID (id on the customer object). Accepts only the settings defined in the request schema, using the same field names and nesting that GET returns. Every field is optional and only the fields sent are changed; nested objects are merged, not replaced. An empty body, an empty nested object, or an unknown field is rejected.

Some settings are not available to every organization (for example Invoice Rover depends on the plan). Sending any value for a setting that is unavailable to the organisation returns 400 and the detail names the setting and the reason. Returns the updated customer in the same shape as GET.