[Vuejs]-Framework7 Vue promise postJson CORS issue

Your GET requests will be generating simple requests, but POSTing JSON requires a non-safe Content-Type request header so will require a preflight OPTIONS request.

The API is failing to respond to the preflight in an acceptable way. The error message will tell you precisely how (typically it will respond with an unacceptable status code (such as a redirect or error) or will have missing or wrong Access-Control-... headers.