Vow of Enmity requires you to see the target.
Vow of Enmity says:
As a bonus action, you can utter a vow of enmity against a creature you can see within 10 feet of you, using your Channel Divinity.
If you read this ability from the character sheet on DnDBeyond, the phrase “you can see” is notably absent from the description:
This is a mistake in DnDBeyond ...