What's the actual way to unblock a number?

iphone's different again: settings, phone, blocked contacts (newer ios puts phone inside apps first), then edit and the red minus. they don't get told either way.

Phone app, three dots top right, Settings, then Blocked numbers - tap the x next to the one you want back. Worth checking the Messages app separately, because it keeps its own block list under spam and blocked, and people unblock in one and then wonder why the texts still don't arrive. Same path on Samsung, the menu is just called Block numbers there.