Check your email first
The approval goes to the address you gave in the application. Check your spam folder before assuming something went wrong.
No printable document is issued: the authorisation is recorded against your passport.
What you need
The passport number you applied with, and your personal details exactly as you entered them.
If you applied with a different passport, the check will not find it.
If it takes longer
Most decisions arrive within 1 day, but allow up to 3 working days. If it takes longer and your departure is close, contact the official channels.