Charge a fee for Cash on Delivery
Shopify doesn't add fees to payment methods, so the fee goes into a shipping rate.
- In Settings › Shipping and delivery, add a shipping rate that includes the fee and has "Cash on Delivery" in its name, for example "Cash on Delivery (+Rs 300)".
- In PayGate, create a rule from Configure cash on delivery fee. It shows Cash on Delivery only when a shipping method containing "Cash on Delivery" is selected.
- Use Test this rule, then try it at checkout: pick the COD rate and check that Cash on Delivery appears with the fee.
Fees are flat amounts. For tiered fees, add several COD rates with different cart value ranges in your shipping settings.