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Connect a serviceHow to connect Mollie to Shopify Flow

How to connect Mollie to Shopify Flow

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Connect Mollie to Shopify Flow with HMAC-verified webhooks. Step-by-step setup, trigger checks, and troubleshooting tips included.

Mollie is a European payment provider. Its next-generation webhooks are signed; the classic payment webhooks are not. Workflow Webhooks turns that call into a Shopify Flow trigger, so your store can react to it: tag a customer, add an order note, send an internal email, update a metafield - anything Shopify Flow can do.

This guide sets up the whole path - Mollie sends, Workflow Webhooks receives and verifies, Shopify Flow acts - with Mollie's HMAC signature checked on every request, so nothing but Mollie can start your workflow.

What you can build

  • Tag a Shopify customer who paid through a Mollie payment link.
  • Add an order note when a Mollie refund goes through.
  • Email your finance team when a payment fails on a high-value order.

Typical events to send: payment-link.paid, payment.failed, a refund is created.

Before you begin

  • Workflow Webhooks installed on your Shopify store.
  • Shopify Flow installed, which is free from the Shopify App Store.
  • An account on Mollie with permission to create webhooks.

Step 1 - Create the webhook in Workflow Webhooks

  1. Open Workflow Webhooks -> Webhooks -> Create webhook and give it a name you will recognise in Flow, such as Mollie events.
  2. Under Authentication, choose HMAC.
  3. Under Signature provider, pick Mollie. The app fills in the header, algorithm, signed payload and replay window for you - there is nothing else to configure.
  4. Leave the secret empty for now and Save. Copy the webhook URL shown on the page.

See Authentication for the other authentication modes, and Payload mapping and Flow variables for choosing which fields reach Flow.

Step 2 - Add the endpoint in Mollie

In the Mollie Dashboard, create a next-generation webhook subscription with the URL you copied, and copy its signing secret.

How to find your Mollie signing secret

The signing secret of the next-gen webhook. Classic Mollie webhooks are not signed at all.

Mollie's own documentation on webhook signatures has the exact wording and screenshots for your account.

Paste that secret into the webhook's Secret field in Workflow Webhooks and save. From that moment every Mollie delivery is verified before it reaches Flow.

What this checks

What Value
Signature header X-Mollie-Signature
Where the signature sits The header value, after the prefix sha256=
What is signed {body}
Signature HMAC-SHA256, hex encoded
Timestamp Not used by this sender
Replay protection None - this sender does not sign a timestamp, so every valid signature stays valid
The secret Used as plain text. Paste it exactly as the sender shows it

In the signed payload, {body} is the raw request body, byte for byte.

A request that fails any of these is rejected with 401, is recorded in History and troubleshooting, and never starts a workflow.

Step 3 - Build the Shopify Flow workflow

  1. In Shopify Flow, create a workflow and choose the Workflow Webhooks trigger.
  2. Press Record events, then send a test event from Mollie (or use Send test in Workflow Webhooks) so Flow learns the shape of your data.
  3. Every webhook you own fires the same Flow trigger, so add a first condition on the webhook id to keep this workflow to Mollie only. The id is shown on the webhook page.
  4. Add your actions - tag a customer, add a note, send an internal email, update a metafield.
Shopify Flow's Select trigger panel with Workflow Webhooks opened, listing Webhook Trigger and Sync Webhook Trigger
In Shopify Flow choose Select a trigger, open Workflow Webhooks and pick Webhook Trigger.
A Flow condition: Webhook id is equal to the ID of one webhook
The first step of every workflow: a condition on the webhook ID, so the workflow only runs for this webhook.
The finished workflow: Webhook Trigger, a condition on the webhook ID, then Send internal email on the True branch
The finished workflow: trigger, condition on the webhook ID, then your action on the True branch.

Step 4 - Test it end to end

Trigger a real event in Mollie. In Workflow Webhooks -> History you should see the invocation with status Success. If the signature was wrong you get a failed entry with the reason instead, and Verifying signed webhooks explains the signature tester that shows you exactly which step failed.

One invocation opened in History with its request headers, payload, status, duration and identifiers
A delivered event in History: status Success means Shopify Flow accepted it.
The signature does not match

In this order: the secret (the most common cause - an extra space, or a key from the wrong environment), whether the sender is using a different endpoint's secret, and whether anything between Mollie and the app rewrites the body. Signatures cover the raw bytes, so a proxy that re-formats JSON breaks them. The signature tester on the webhook page shows the exact text that was signed.

I get 401 on every request

Check that the webhook's authentication is set to HMAC with the Mollie provider selected, that the secret is filled in, and that Mollie is posting to the URL exactly as the app shows it, including the code at the end.

Nothing appears in History

The request never arrived. Re-check the URL in Mollie, and look at Mollie's own delivery log for the response it got. A 404 means a wrong or deleted webhook, a 429 means you are over your plan's invocation limit - see Plans and usage.

The workflow runs for the wrong events

Every webhook in your store fires the same Flow trigger. Add a condition on the webhook id as the first step of the workflow, or narrow the events you send from Mollie.