无法获取Reddit API访问令牌以访问用户信息，求协助排查Postman问题

Hey there! Let's troubleshoot why you're stuck getting a Reddit API access token in Postman—this is super common, so let's break down the most likely issues step by step.

Before diving into Postman, make sure your app is configured correctly on Reddit's Developer Portal:

• Pick the right app type: If you're trying to fetch user-specific info, you’ll need either a web app (for redirect-based flows) or a script app (for password-based flow, only for your own Reddit account or trusted users). Avoid using a "native app" unless you’re building a mobile/desktop app.
• Match the redirect URI exactly: The redirect URI you entered in your Reddit app settings must be identical to what’s in Postman—including http/https, port numbers, and even trailing slashes. For example, if you set http://localhost:3000/callback in Reddit, don’t use http://localhost:3000 or https://localhost:3000/callback in Postman.

Let’s make sure every part of your request is set up properly:

For the Access Token Endpoint (POST https://www.reddit.com/api/v1/access_token) #

• Headers are non-negotiable:
  • Add an Authorization header with the value Basic {base64-encoded string}. To get this string, take your Reddit app’s client_id and client_secret, combine them like client_id:client_secret, then encode that pair to base64. Don’t add quotes around the encoded string!
  • Set Content-Type to application/x-www-form-urlencoded—this is required for Reddit’s token endpoint to parse your parameters correctly.
• Body parameters depend on your flow:
  • If using the Authorization Code Flow (most common for user data):
    • grant_type: Must be authorization_code
    • code: The authorization code you got from the initial GET https://www.reddit.com/api/v1/authorize request (note: this code expires in 10 minutes, so grab a fresh one if it’s old)
    • redirect_uri: Same exact URI as your app setup and authorization request
  • If using the Password Flow (only for script apps):
    • grant_type: Must be password
    • username: The Reddit username of the account you’re accessing
    • password: The corresponding password for that account

If you’re getting an error response, here’s what it usually means:

• invalid_client: Your client_id/client_secret is wrong, or the Authorization header’s base64 encoding is messed up. Double-check the credentials from your Reddit app, and re-encode the client_id:client_secret pair to make sure you didn’t make a typo.
• redirect_uri_mismatch: As mentioned earlier—your redirect URI in Postman doesn’t match what’s in your Reddit app settings. Fix this and try again.
• invalid_grant: Either your authorization code is expired/invalid, or you used the wrong grant_type for your flow. For password flow, this could also mean the username/password is incorrect.
• 429 Too Many Requests: Reddit is rate-limiting you. Wait a few minutes before sending another request.

If you can provide a screenshot of your Postman request, be sure to highlight these key areas for faster debugging:

• The full request URL
• The Authorization and Content-Type headers
• All parameters in the request body
• The exact error response (status code + message)

内容的提问来源于stack exchange，提问作者ravi prakash