A reminder about SD Notary and "unknown problem with altool"

I was getting the “unknown problem with altool” message from SD Notary this morning, and was tearing my remaining hair out until I came across this suggestion from Shane Stanley in an earlier thread:

try going to Xcode Preferences -> Locations, and check the right version of Command Line Tools is selected

The version was blank in my copy of Xcode, but clicking on the blank field brought up the correct version number, and then the problem went away. Time to thank Shane once again (for the hundredth time, maybe) for solving problems.