My day to day browser is a hardened Firefox (plenty of about:config tweaks, resistfingerprinting, ublock origin, temporary containers etc). For signing up to Oracle Cloud I used a tmpfs based Chromium browser (ie: completely fresh, factory defaults) to avoid issues resulting in my hardened browser. Oracle cloud refused to accept my credit card with a bogus error message saying something about fraud and/or incomplete/incorrect personal details. I searched for the error message and someone on a random website mentioned about having issues with Chrome and to try Firefox. I found that quite unusual as it's usually the other way around but I tried using my day-to-day hardened firefox and instantly worked and account activated within minutes. Go figure.