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Dynamic Flows — prefill answers and load live options

📝 WhatsApp FlowsLevel: Advanced⏱ 6 min

🎯 Goal

Make forms smarter: returning customers see their details filled in. You don’t run any server yourself.

🧰 What you need

  • A Flow in the editor
  • Your platform administrator has set the Meta app secret (it is already set on meapi.in)

Static vs dynamic

Section titled “Static vs dynamic”
  • Static Flows contain everything in the form itself. They’re simple and the default.
  • Dynamic (data endpoint) Flows talk to a server while the customer fills them in. MeAPI hosts the encrypted endpoint and uploads the public key to Meta for you (one key for your account, uploaded to each number).

Turn it on

Section titled “Turn it on”
  1. In the Flow editor open Settings and switch on Dynamic (data endpoint). The form card then shows a dynamic badge.
  2. On the Build tab, each Short answer and Long answer gets Prefill from the contact: pick Name, WhatsApp number or a contact field. Leave Don’t prefill for the rest.
  3. Dropdown, Single choice and Multiple choice questions can load options from your own https:// URL that returns JSON like [{"id":"jaipur","title":"Jaipur"}].
  4. Save, Sync to Meta, test, then Publish.

When the form opens, WhatsApp asks our endpoint for the first screen. We answer with the contact’s saved values, encrypted with Meta’s scheme. The customer only confirms or edits.

Security

Section titled “Security”
  • Every request from Meta is checked against the app’s signature. Bad signatures are refused (status 432).
  • Payloads are encrypted (RSA + AES-GCM). Undecryptable requests are refused with status 421, which makes Meta re-fetch the public key automatically. The endpoint never answers in plain text.
  • Answers are tied to the contact by a one-time flow token registered when the form was sent.

What’s next

Section titled “What’s next”

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