In your Shopify store, navigate to Settings > Payments.
In the Additional Payments section, click on Add Payment method:
Click the Search by provider tab, search for Mollie - iDeal and select the option:
Install the payment method:
You will be redirected to Mollie where you will have to:
Sign in to your account (if not logged in already).
Link a merchant account that will be used by Shopify to power iDeal. Make sure that if you have multiple merchant profiles in Mollie, you are linking the one with iDeal, Bancontact and SEPA Direct Debit enabled.
When you return to Shopify, make sure the iDeal toggle is turned on. And the Test mode toggle is turned off.
Click Activate:
Repeat for Mollie - Bancontact if needed.