Hi @Chalani_Peiris, there is a way to generate an access and refresh token without going through the OAuth flow. If you go to https://accounts.infusionsoft.com, there will be an “API Access” link next to each of your Infusionsoft accounts. Click on that link, enter your client id and secret from here, and an access and refresh token will be generated.
Edit: I would also recommend putting the access token in the auth header rather than as a url parameter. See the “Making Requests” section of the REST documentation for more info.