Flutter使用Google API发送邮件时遇400解析错误求助

Hey there! Let's get this sorted out quickly. That 400 error is spelling out exactly what's going wrong: the API you're calling only accepts JSON-formatted request bodies, but your POST request is sending form-encoded data (the default behavior for many HTTP clients if you don't specify otherwise).

Here's how to fix it step by step: #

1. Set the correct Content-Type header
   Your request must include the header Content-Type: application/json — this tells the server to expect JSON data instead of standard form fields.

2. Convert your request body to a valid JSON string
   Instead of passing key-value pairs as form data, serialize your payload into a proper JSON string. For example, if you're using JavaScript:

   // Correct implementation
   fetch('your-target-api-url', {
     method: 'POST',
     headers: {
       'Content-Type': 'application/json',
       // Add any other required headers (like auth tokens) here
     },
     body: JSON.stringify({
       // Your request data structured as JSON
       scope: 'send-email',
       recipient: 'user@example.com',
       subject: 'Test Email'
     })
   })
   

3. Validate your JSON syntax
   Since you mentioned uncertainty about your JSON format, use a free tool like JSONLint to check for syntax errors (missing commas, unclosed quotes, mismatched brackets, etc.). Even a tiny typo here will cause parsing failures.

Quick troubleshooting checks: #

• If you're using tools like Postman, make sure you've selected the "raw" body type and set the format dropdown to JSON (not form-data or x-www-form-urlencoded).
• Avoid mixing form data and JSON — don’t use FormData objects alongside JSON.stringify in the same request.
• Double-check your API docs to confirm it explicitly accepts JSON payloads (most modern APIs do, but it’s always good to verify).

内容的提问来源于stack exchange，提问作者rafaelcb21