I have used Gazelle a couple times and either got paid on or ahead of time. However, I have never used sears.gazelle.com I just go to gazelle.com (not saying that is the issue). Have you given them a call or sent an email?
Yup, I've emailed them 3 times since their failed payment. We'll see what their excuse is this 3rd time. Maybe Santa's reindeers were delayed in a winter storm?