How to find deactivated relay ID for apps

I unintentionally used ‘hide my email’ when logging into an App I bought. So the app vendor does not know my real email id. The relay caused problems when resetting a password. I discovered the privaterelay.appleID option for the app and deactivated/deleted it. But I did not take a screenshot first so now I have no idea what that relay ID was. The app vendor can find no subscription under my real email ID…. How can I find out what the relayID was? This is not an iCloud/Safari relay ID that I’m talking about.