Assigns or updates values to customer fields. The fields must already exist, if the customer does not exist, create it.
Fields that do not exist will be ignored.
If a formatting error occurs in any of the fields an error code 400 will be returned and in that case no modification will be made.
When using a field of type datetime, set the date according to ISO 8601 standard. E.g: 2021-10-22T10:46:23.897Z