Try this first
Have it sent again
Open lonelyduck.io/canto/activate and press Email my license. It goes to the address you bought with. In Canto, Settings › Account › Lost your license? does the same. Open the email on your Mac and click the activate link; Canto asks before it activates anything. Or paste the license (it starts canto-license-v1), or the whole email, in Settings › Account.