Fitbit Api "Missing 'grant_type' parameter value" issue

Hey I am trying to get Fitbit API oauth2/token access but its throwing the following error

There was an issue setting up your call.

Raw response for the API 
Status code 400
{"errors":[{"errorType":"invalid_request","message":"Missing 'grant_type' parameter value. Visit https://dev.fitbit.com/docs/oauth2 for more information on the Fitbit Web API authorization process."}],"success":false}

Here are the screenshots
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I am properly passing all the parameters and headers but still showing this. I tried to use various variations but no success.

Here is the Fitbit API documentation

I tried to add the grant_type parameter in call then it shows the following error

In this case, it shows Expecting: application/x-www-form-urlencoded. I tried to look on forum regarding this but couldn’t find any proper solution.

Need help to solve this. If someone has implemented this call or knows the solution. I will be thankful.

Regards
Muhammad Ammar

This may just be me but 9/10 times I create the oAuth flow manually instead of using bubbles built in oauth2 feature. It very rarely works as you want in my experience and most APIs I’ve needed to do it on (Google, ticktock, outlook, etc) all tend to work better when done manually.

Manually: button click to go to auth URL. Watching redirect URL for code or token, saving that and storing refresh times and refreshing when necessary.