Using the CRSurveyAPI submitSurvey method, the survey isn't being submitted successfully when an optional multiple-select question isn't answered. The API request fails with the error code 1732 and the following error message:
Invalid Selection: Please select from the available options for this question.
This occurs when a null value is sent for the optional multi-select question. Since that question only accepts values explicitly listed in the question choices, a null value is not acceptable. To successfully submit a survey with an optional multi-select question, remove that question parameter from the API request if no value is selected.