AppStore: The operation couldn’t be completed. (com.apple.commerce.client error 500.)

[oliversl]

Its al old post, but for me, my solution was:

1. Logout AppStore
2. Search in Library/Preferences and in Library/Cache the filename "AppStore" then delete (6 in total), empty Trash
3. Reboot to reset the NVRAM: https://support.apple.com/en-us/HT204063

HTH