Why didn't I receive this two-factor authentication code?

I logged into a MacBook to complete an app purchase and was asked to enter a 2FA (Two-Factor Authentication) code, with the dialog stating that I needed to verify from a trusted device (presumably the iPhone on the account). However, no 2FA code never popped up, and I had to get a text after several retries. What went wrong, or am I doing something incorrectly? iPhone is Version 11.2.6, Mac is OS X 10.11.6. Two-Factor Authentication is enabled.