Most of the time "into" is what you want, which is why the two-word version looks like a typo when it is actually correct. "In to" arises when "in" belongs to the verb before it and "to" belongs to whatever follows — they are neighbours, not a unit. The classic example, "turned himself in to the police," means something quite different from "turned himself into the police."
A single preposition expressing movement toward the inside of something, or transformation.
Two separate words. "In" completes the verb; "to" belongs to what comes next — often an infinitive.
Quick way to remember
Check whether "in" belongs to the verb. If the verb is "log in," "give in," "turn in" or "come in," then "in" is part of the verb and "to" is separate. If the sentence is about going inside something or becoming something, use "into."