You can use this API to lookup the answer that customers gave to questions for custom fields associated with a particular product. If you don't know a customers product ID, you can look it up using the customer subscriptions API, and then call this API in sequence if necessary.
This API uses only Customer and Product IDs as parameters but as each Customer ID can only hold one subscription, responses will be specific to only one subscription.
You'll need to use this API to return the custom field response ID if you want to use the Update customer response API.
The unique identifier for an individual customers response to a question
The unique identifier of the custom field
The type of custom field; SingleLineTextField = 0, MultiLineTextField = 1, CheckboxField = 2, DatePickerField = 3, NumbersField = 4, DropdownField = 5
Title of the custom field
Description of the custom field
A comma separated list of option titles for DropdownField type
Is the custom field compulsory; true or false
The customer response to the custom field