Why it's not a match: untangling the "lower then" error

What kind of error is it?

Homophone and grammatical error

Why do people make this mistake?

People often confuse "then" and "than" because they are homophones, words that sound similar but have different meanings, and are used in different grammatical contexts.

What is correct?

The correct phrase is "lower than". "Than" is used for making comparisons, while "then" is used to indicate time or sequence.