Use numbers when the meaning is intentional
A number tied to the company story, product, or established brand can work well. The key is that users know whether to type the digit or spell the word.
Avoid substitution gimmicks
Replacing words with numbers simply because the preferred domain is taken often makes the brand harder to say and remember.
Test spoken navigation
Say the domain aloud to someone who has never seen it and ask them to type it. That quickly exposes ambiguity.