When donors give us money, we want to hide banners for them on wikiPedia.org subdomains. We previously were doing that on a thank you page at donate.wikiMedia.org by including <img> tags sourcing Special:HideBanners on wikiPedia.org. Browsers now reject third-party cookies so we started showing the Thank You page at donate.wikPedia.org (T251780).
Unfortunately mobile donors with apps installed are now seeing the app launch instead of a Thank You page, and are getting an error instead of the TY page content. This has prompted a few hundred duplicate donation attempts.