To configure your Shopify store to work with Affirm, you will need to follow the steps below.
Only the Account Owner can adjust the payment methods for a Shopify store.
1. Go to Settings > Payments
2. Click on "Choose Alternative Payments"
3. From the Alternative Payment Providers screen, select Affirm by clicking on it.
4. Enter your Public and Private API keys which you were issued when you signed up for Affirm and then Check "Enable Test Mode" before clicking on "Activate Affirm"