#1 - People can manually enter the coupon on the Checkout Page. For this you don't need to do anything else other than providing the coupon code to them.

#2 - You as the product seller can automatically apply the coupon using a link.

Simply attach the following string AT THE END of the ORDER URL:

where coupon-code is the actual coupon code.

E.g. You have this coupon code:

Scenario 1
Suppose your ORDER URL is:

Then the coupon link would be:

Scenario 2
Suppose your ORDER URL is:

Then the coupon link would be:

Did this answer your question?