Need to update second Apple ID
Somehow I have ended up with two Apple ID's. Cannot update credit card on Macbook for the "second / newer" Apple ID as it must be done on an iOS device but my iPhone won't let me add the second Apple ID as the "second / newer" Apple ID email is showing as taken and cannot sign out of my "first / primary" Apple account ID on iPhone without first adding a replacement Apple ID email? This seems counterintuitive, any suggestions how to solve this issue please?
iPhone XR, iOS 17