I am using the GitHub API to authenticate a user, and get an authentication code. Now, however, I have to exchange this authentication code for an access token from the user’s github account.
I’ve followed the documentation, but it’s not working. I am getting different errors depending on what I try.

    const tokenUrl = 'https://github.com/login/oauth/access_token';

const headers = {
  'Content-Type': 'application/x-www-form-urlencoded',
  'Accept': 'application/json'
};

   const params = new URLSearchParams();
    params.append('client_id', clientId);
    params.append('client_secret', clientSecret);
    params.append('redirect_uri', redirectUri);
    params.append('code', code);

try {
      const response = await fetch(tokenUrl, {
        method: 'POST',
        headers: headers,
        body: params,
        mode: 'no-cors'
      });
    
      if (response.ok) {
        const parsedResponse = await response.json();
        if (parsedResponse) {
          const accessToken = parsedResponse.access_token;
          console.log('personal access token', accessToken);
          // Use the access token to make API requests on behalf of the user
        } else {
          console.error('Failed to parse response');
        }
      } else {
        console.error('Failed to fetch token:', response.status, response.statusText);
      }
    } catch (error) {
      console.error('Error fetching token:', error);
    }

This gives me this error: Failed to fetch token: 0

When I try this:

const GITHUB_HEADERS = { 'Authorization': 'Bearer ghp_...' };
    const GITHUB_BODY = {
      "client_id" : clientId,
      "client_secret" : clientSecret,
      "redirect_uri" : redirectUri,
      "code" : code
    };

    const response = await fetch(tokenUrl, {
      method: 'POST',
      headers: GITHUB_HEADERS,
      body: JSON.stringify(GITHUB_BODY),
       mode: 'no-cors'
    })

    if(response) { 
      const parsedResponse = response.json()
      console.log('response successful', response.json())
      if(parsedResponse) { 
        //const accessToken = parsedResponse.access_token;
      }
    }

I get this error:

POST https://github.com/login/oauth/access_token net::ERR_ABORTED 404 (Not Found)

response successful Promise {<rejected>: SyntaxError: Unexpected end of input
    at TemplatesPreview.getUserToken (http://localhost:6262/di…}

Uncaught (in promise) SyntaxError: Unexpected end of input (at templates-preview.tsx:145:1)
    at TemplatesPreview.getUserToken (templates-preview.tsx:145:1)

Any ideas?