Shopify doesn't allow adding a fee directly to a payment method. The solution is to create a special shipping rate where the Cash on Delivery fee is already included in the price.
This guide will walk you through setting up this dedicated shipping rate.
1. Go to Settings
From your Shopify Admin dashboard, navigate to Settings in the bottom-left corner.
2. Open Shipping and delivery
In the Settings menu, find and click on Shipping and delivery.

3. Manage Your Shipping Zones
Click on the "General shipping rates" section. This will show you your existing shipping profiles.

4. Add a New Rate
Find the shipping zone where you want to offer COD and click Add rate.
> Note: If you don't have a shipping zone for a specific country or region yet, you'll need to create one first by clicking "Create shipping zone".

5. Configure Your COD Rate
A new window will appear. This is the most important step:
Rate name: Give it a clear name that your customers will understand, for example, "Courier - Cash on Delivery" or "Express COD Shipping".
Price: Set the total shipping cost, including your standard shipping fee plus the extra COD fee. For example, if standard shipping is $5 and your COD fee is $3, you should enter $8.

6. Save Your New Rate
Once you've configured the name and price, click Done, and then click the Save button at the top of the page.
Excellent!
You have successfully created a shipping rate that includes your COD fee. Now you're ready for the final step: connecting everything in the Progus COD app.
Next Step: [Link to Article 3: How to Connect Your Shipping Rate in the Progus COD App]