The Progus integration guide tells your storefront to send the cart to the Progus API when a buyer clicks the iDEAL button. Progus gives you instructions for your developer or for an AI builder such as Lovable. The storefront then sends its cart to Progus and sends the buyer to a ready checkout.
Before you start
Connect Mollie and turn on the Mollie checkout button.
Without both, the API still works, but every buyer is sent to the normal Shopify checkout.
Step 1: Open the Mollie settings
Go to Settings → Integrations.
Step 2: Open Mollie
On the Mollie card, click Configure.
Step 3: Turn on the checkout button
Tick Show the Mollie checkout button.
Step 4: Save the setting
Save the checkout-button changes in the contextual bar.
Step 5: Open the instructions
Open the headless integration guide.
Step 6: Add your shop domain
In Your shop domain, enter the .myshopify.com address from Shopify admin.
Step 7: Copy the instructions
Click Copy for LLM.
Step 8: Give them to your storefront
Paste the instructions into Lovable, or send them to your developer.
Step 9: Place a test order
Place one real iDEAL order.
Step 10: Check the checkout
Confirm that the checkout shows iDEAL and the subscription price.
Step 11: Check an abandoned checkout
Start a checkout, go back without paying, and check that the cart is unchanged.
If it does not work
Prepaid plans, plans from other apps and carts that are not in euros go to the normal Shopify checkout automatically.
If the API answers variant_not_found and your products are published only to your headless channel, ask your developer to send the public Storefront token as storefrontAccessToken.
What to do next
Stuck on any of this? Open the chat in the bottom right corner of the app and we will help you set it up.
Last verified on 2026-10-28 against progus-subscriptions 4db5256b (kb-ref: add-an-ideal-button-to-a-headless-storefront).