From the Imgur API docs...

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Answering here to provide a canonical answer in the imgur tag for this nonsense.

All the API examples in the documentation use some form of multipart/form-data request body payloads. Eg

var myHeaders = new Headers();
myHeaders.append("Authorization", "Bearer {{accessToken}}");

var formdata = new FormData();

var requestOptions = {
  method: 'PUT',
  headers: myHeaders,
  body: formdata,
  redirect: 'follow'
};

fetch("https://api.imgur.com/3/account/{{username}}/settings", requestOptions)
  .then(response => response.text())
  .then(result => console.log(result))
  .catch(error => console.log('error', error));

and

curl --location --request POST 'https://api.imgur.com/oauth2/token' \
--form 'refresh_token="{{refreshToken}}"' \
--form 'client_id="{{clientId}}"' \
--form 'client_secret="{{clientSecret}}"' \
--form 'grant_type="refresh_token"'

With the exception of any upload related endpoints, this is ABSOLUTELY INCORRECT. Passing data as multipart/form-data requires the API to handle that request content-type and guess what, the Imgur API does not.

What they do accept is application/x-www-form-urlencoded.

• In Postman that's the x-www-form-urlencoded option, not form-data
• In cURL that's the -d option, not --form
• In JavaScript that's URLSearchParams, not FormData