it may help to use the HTTP tool on Make and call VAPI with the API you may get better results. Also 400 can mean an issue with the formatting of the posted JSON etc, maybe some issue with the data being posted from the Excel Sheet? I get 400 if the JSON sent to VAPI is not correct, corrupted or incompatible with the API itself. In this case maybe the Sheet has data that could corrupt the JSON sent to VAPI.