On the checkout page, you enter the code# into the box just after "Gift Cards or Summit Bucks" and then enter the date "12/31/2022" into the issue/expire date box. Click on "Apply" and it should show a complementary discount near the bottom of the checkout page.
Thanks for the coupon. I used it this morning, success!
Note 1): Don't put the code in the "Promotional Code" box on the cart page (see above).
Note 2): I had to logoff Summit and check out as a guest. Otherwise it kept trying to use my ProShop discount (which does not allow this discount).
Regular prices $2,154.49
Complimentary discount $215.46
Total before tax $1,939.03
ProShop total before tax would have been $2,078.30