Hola Kaly

When we use "invitar a alguien" (to invite someone), the "someone" is a direct object, so when we say "invite them", that them is a direct object pronoun, i.e. "los". "Les" is the indirect object pronoun. Having said this, bear in mind you may see sometimes "les" used as a direct object pronoun" but this is considered incorrect. This is called "leísmo". You can read about this in this Kwiziq article.

I hope it helps.

Saludos cordiales

Inma