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Formbase stores submissions as a JSON object where each key is the name attribute of a field. Most HTML inputs work exactly as you expect, but some types (checkbox groups and multiple inputs) have special considerations. Use this reference to pick field names and understand what shows up in your submission data. 
<input name="full_name" type="text" />
<input name="email" type="email" />
<input name="age" type="number" />
<textarea name="message"></textarea>
Each field becomes a string value in the submission data.
<label><input type="radio" name="plan" value="basic" /> Basic</label>
<label><input type="radio" name="plan" value="pro" /> Pro</label>
Only the selected value is submitted. The key is plan and the value is the chosen option.
<label><input type="checkbox" name="newsletter" value="yes" /> Subscribe</label>
If checked, the value is sent. If unchecked, the key is omitted entirely.
<select name="country">
  <option value="us">United States</option>
  <option value="ca">Canada</option>
</select>
The selected option value is stored under country.
<input name="resume" type="file" />
Files are uploaded and stored as URLs. Formbase sets either the file or image key based on the MIME type.

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Multiple values with the same name

When using multipart/form-data, repeated keys collapse to the last value. If you need arrays (for example, multi-select or checkbox groups), submit as JSON instead. 
await fetch('https://formbase.dev/s/YOUR_FORM_ID', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({ tags: ['design', 'growth', 'product'] }),
});
JSON submissions are best when you need structured data or arrays. Browser form posts are best for simple, classic form flows.