Trying to add to my system has been incredibly frustrating

I'm moving to a new house Memorial Day weekend, and I wanted to add some equipment to my SimpliSafe system. I saw a discount code online for 30% off, but even though the site said the coupon had been applied, it would not actually reflect the discount on the order. I called in to ask about it, and the rep I spoke to (who was very friendly, tried her best, and is not at fault for any of this) said she could create an order with a 30% discount on the new equipment and send me a link to check out with Affirm. I received the email with a price breakdown and the 30% discount applied, all in writing in the email. When I click the link, however, the discount was not applied in the shopping cart. She offered to issue a refund if I completed the purchase, but that makes things way more complicated than they need to be, especially with the Affirm payment schedule. I'm not even sure how that would work with Affirm.

I have been happy with SimpliSafe since switching from ADT, but I'm honestly not feeling super confident about continuing to rely on the company for my security when something this simple can't be worked out.