StoreHippo provides the support to set the payment methods based on the order quantity. For different order quantities, you can set different payment methods.
You have two payment methods defined i.e. COD and Online Payments. When the customer buys less than three quantities of a product, you want to offer COD. On the other hand, when the customer buys more than three quantities of a product, you want to offer an online payment method. You can set this by adding order quantity based payment methods.
When order quantity is less than three:
When order quantity is greater than three: 
To set the payment method based on the order quantity, follow the steps mentioned below:




Now, when the order quantity will be greater than three the online payment option will be provided to the customer. In the same way, you can set the COD payment option for order quantity less than three.