There are number of differences between promotional code vs coupon code, but they can be used interchangeably in many circumstances.
Below are a number of examples of the variations between difference between coupon code and promo code.
Generation of the bulk
Vouchers can be generated in full, whereas Coupons can only be produced one at a time.
It makes coupons valuable for major company purchases. Imagine, for example, that a company wants to purchase 500 licenses for your course and that they require a unique code for each of its employees.
With 1 voucher, you can easily produce 500 unique codes and export.csv of the codes that you will give to your client.
It will take you a very long time to do so with a voucher, so you will have to bargain with this business, offering them a coupon code of 500 uses.
Connection to Goods and Interaction
Vouchers can provide access to multiple courses and memberships in one purchase, and coupons can only give access to one course or one membership at a time.
If you wanted to give the student access to five different courses, you could give the student a voucher that gives them access to the five redemption courses.
The borrower may collect this voucher and have access to all five courses at once.
You would have to give the student five different coupons to accomplish that and they would have to go through the checkout process five times.
Alternatively, the vouchers may not have to be connected to a course or membership. If you were to send a student 100% of their pick, you might do so with a discount, but not a coupon.
Vouchers can only be exchanged during new user registration (when enabled) and on the student dashboard.