Confirming Rod with the addition that I changed my AppId from com.xxxx.* to just *
I had same problem today with building a new iOS App. Followed Jonathan Clark’s suggestion. Opened a new Project in Xcode, added my profile to Build Settings/Signing/Development Team dropdown. Then Product/Build For/Testing - the build failed but now the app build’s OK in Xojo.
Same problem, and building a new iOS project in Xcode worked for me: