This issue was fixed in TypeSquare Desktop Manager Ver.2.0.4 and later.
If you are using an earlier version of TypeSquare Desktop Manager, please update to the latest version.

Please download the latest version of TypeSquare Desktop Manager from the following page. You will first need to log in to TypeSquare web site. Please download the installer from “for Mac” button in this page:
https://typesquare.com/dlselect/tool_install

After you install TypeSquare Desktop Manger, please try the following steps if you receive the error "Font registration failed" in TypeSquare Desktop Manager on macOS 10.13 or later:
1. Go to Apple menu > System Preferences > Security & Privacy
2. Go to General tab on the Security & Privacy window
3. Unlock if you cannot make changes
4. Select "App Store and identified developers" under "Allow apps downloaded from:"
5. Click "Allow" button next to "System software from developer "Morisawa Inc." was blocked from loading" message

Please try the following additional steps when the "Allow" button in the STEP 5 as shown above does not appear:
1. If this button does not appear, please restart your OS. This button disappears in 30 minutes after the OS restarting.
2. If this button does not appear even after you restart the OS, please uninstall and reinstall TypeSquare Desktop Manager so the button will appear.

Please note that you will need to sign out of TypeSquare Desktop Manager from the Account tab and try to sign in again.

Note:
- If you were using TypeSquare Desktop Manager on macOS 10.12 or earlier and have upgraded your OS to 10.13 or later, you can use TypeSquare Desktop Manager without the error.