This module adds a configurable extra fee for the Magento2 default cash on delivery payment Method. you can add this functionality to add the extra charge for a Magento 2 Cash on Delivery payment method.
After installing Cash On Delivery:
Go to Stores -> Configuration -> Sales -> Payment Methods. There should be a new Configuration "Cash on Delivery Fee" under the Cash on Delivery Payment Method with a default value of 0.0
The Fee total will display in the Checkout and Order totals as soon as the Cash on Delivery Payment Method has been used and the value of the Extra Fee is > 0.