hi, we have just been through the same procedure and here are the findings - discovered by trail and error. TLDR: there is no rollback. when you activate a new payment processing certificate, it warns you that the older certificate will be revoked. ouch. what happens if there is an error? what happens if you've made a mistake generating the certs? what happens if it is peak buying season and you have to disable the apple pay option because you are forced to fix any problems resulting from having to activate the new certificate. a simple switch allowing you to go back and forth between certificates makes much more sense imho. anyway... it takes a few minutes before the new payment processing cert propagates across the web. this caused no end of problems, as our payments failed with a "decoding error". these went away after max 20 minutes. be aware of this. we are a bit unusual as we do the decoding ourselves, rather than use stripe/adyen to do it for us. so you can probably ignore this point. i am sure this is much too late to help, but as this thread was top result for the search: "reactivate" apple pay payment processing certificates, i thought i'd answer for any future reference.