Fillo doesn't currently have a direct Mailchimp integration, so prefill goes through your backend: read the audience member you're authorized to see, then pass selected values into Fillo.
Resolve the member privately
Use a signed-in account or a single-use application link to decide which Mailchimp member can be read. Call Mailchimp from the server with a private credential, and return only the fields the preference form needs.
const initialData = {
email: member.emailAddress,
first_name: member.mergeFields.FNAME ?? "",
product_updates: member.tags.includes("product-updates"),
};Pass this into FilloForm through initialData. A checkbox URL value and an initialData boolean travel in different shapes, so when you already have server data, prefer the typed application object.
Don't treat prefill as subscription state
Prefilled values are editable form answers — nothing more. They don't prove Mailchimp subscription state, and they don't replace the consent process your organization has chosen. Make subscription or preference changes in a server-side Zapier or webhook workflow, with whatever evidence and legal review your context requires.
Use a server-trusted member key. Never take an arbitrary audience ID or subscriber hash from a hidden field and write to it without authorization.
Test synchronization
Cover unsubscribed members, missing merge fields, stale tags, revoked API access, duplicate Fillo delivery, and a Mailchimp failure after the response is accepted. Keep the Fillo response ID in your operational logs — but not message content or private credentials.
Try it
Start with a prompt and your coding agent builds the first form, staged for your review — or open the editor.
Related
- Beta access example: Inspect a live email and preference form.
- Checkbox field: Initialize and validate a preference choice.
- Zapier: Connect Fillo responses to a Mailchimp action.
- Build a GDPR consent form: Record versioned choice context without treating a form as legal advice.