What specifically is not "found"? Is it NPM? If so, check your PATH
variable.
Since you are using a Mac, it should be here:
/usr/local/bin/npm
Also, this is a very generic and common question, please do some more research before posting here.
Edit: As per my comment below.
Are you passing $:
at the start of that command? In most documentation, this refers to the shell command prompt and should not be included in the command.
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