Survey not imported to Qualtrics but process was 100%

I created a survey template, could encode survey response from Qualtrics and import survey data from local csv file as survey responses . Therefore, the survey is active and functional.
However, when I tried to use Qualtrics API, https://iad1.qualtrics.com/API/v3/surveys/{0}/import-responses'.format(surveyId), to upload (import) a local survey csv file to Qualtrics, the API calls showed 100% completion of the process and no error, but Qualtrics shows only the same numbers of the records in the csv file being imported, and the contents of the survey records were empty. I have tested the process for several times, all the survey responses imported have no contents, but increases empty rows.
Is there a problem in the import API? I am wondering the API may not import the survey response contents, but just construct empty response templates?