What does Deuteronomy 18:22 mean?

Here’s how you’ll know: If a prophet says something in the Lord’s name and it doesn’t happen, then the Lord didn’t say it. Don’t be afraid of that prophet. Deuteronomy 18:22 - Modern Text Bible

(The test for a true prophet is whether what they say actually happens. If it doesn’t, they’re not speaking for God, and you don’t need to listen to them.)