You will need 3 API Calls to retrieve the responses:

1. Start Response Export: 
   •Starts an export of a survey's responses. You can define the format in which you want to extract the responses.
   •Documentation Link: https://api.qualtrics.com/6b00592b9c013-start-response-export
2. Get Response Export Progress

   •Retrieves the progress of the response export. Please note you will exportProgressId find the in the Export Responses POST response in the progressID field.

   •Documentation Link: https://api.qualtrics.com/37e6a66f74ab4-get-response-export-progres

   3. Get Response Export File

   •Retrieves the response export file after the file export process completes. 

   •Documentation Link: https://api.qualtrics.com/41296b6f2e828-get-response-export-file

    

   Hope this helps :)