A while back I was buying tickets for a gondola for a trip in Europe and the checkout process failed during payment because their site didn't load their analytics/tracking stuff with proper error-handling, so when my ad-blocker prevented the tracking stuff, their checkout process failed to handle my CC's 2-factor auth and the checkout would fail. Had to contact my CC company and work with the gondola company to tell them what they're doing wrong so they could fix their website code. Pretty sad to know whoever built their stuff actually shipped a checkout flow (for a VERY popular tourist destination) without testing with ad-blockers enabled.