Problem with Apple Store app on Mac

Sounds like while you created a new Apple Account you are trying to change the email of the existing Apple Account to the email of the new account. That's not going to work, and is not what you are supposed to do.

You are supposed to sign out of the Apple Account being used for the Mac App Store app on your Mac and then sign in with the new one you created. Not try to change it's email address.

Open the Mac App Store, click on the Store Menu at the top, and then on Sign Out to sign out of the Mac App Store. Then click on Sign in and enter the new Apple Account.

Do note, any apps downloaded with the previous account will remain tied to that account and require it to update. You will need to delete those Apps and redownload them with the new account.

I believe some corporate Apple Accounts are tied to a business and cannot be used outside your business. You have now created a new account. Only after a very long wait period can you use an email address used as an ID for one account as the email address for a new account. Your apps also are tied to the old account. You will need to sign into your new account in order to use the App Store (oh, the "Apple Store" is something completely different). Go to the App Store app on your Mac. In the menu at the top click on Sotre, then at the bottom of the new tab click on Sign Out. Sign in with your new account.

You can continue to use any apps you have downloaded already but should you wish to update them or re-download them you will need to use the old account. If you can no longer do that then you will have to delete the apps and download them using your new account.