I am trying to generate Access Token using the URL: https://accounts.zoho.in/oauth/v2/token
and sending    {"client_id"}
                 {"grant_type"="refresh_token"} in parameters
in the response I am getting {"error":"access_denied"} ans sometimes {"error":"invalid_code"}
Even if I am trying to generate the access token for the first time I am getting these errors for different zoho crm accounts.
Please suggest if I am doing anything or any step wrong. Please guide me.

            Zoho DataPrep Resources

                Zoho CRM Plus Resources

                  Zoho Books Resources

                    Zoho Subscriptions Resources

                      Zoho Desk Resources

                        Zoho Projects Resources

                          Zoho Sprints Resources

                            Zoho Orchestly Resources

                              Zoho Creator Resources

                                Zoho WorkDrive Resources

                                    Zoho Campaigns Resources

                                      Zoho CRM Resources

                                                  Design. Discuss. Deliver.

                                                  Create visually engaging stories with Zoho Show.

                                                  Get Started Now

                                                      Zoho Writer Writer

                                                      Get Started. Write Away!

                                                      Writer is a powerful online word processor, designed for collaborative work.