I am american so I cannot speak for my british amigos across the atlantic, but here it is always to check in when used by itself but if it is followed by the noun hotel/room it uses the preposition “to” in between to check in and hotel/room (check in (to) (my) hotel)
I think I’m going to check in before my coupon expires.
Why are you going to check in with your grandma still in the car?
Now using the noun hotel in this phrase.
I need to check in to my hotel/room before my coupon expires.
Why are you going to check in to your hotel/room with your grandma still in the car?
More examples in case those were not clear.
I never check in before the valet shows up.
If your famous enough you don’t even have to check in before going to your room, they just know.
Some examples with the into hotel part
I once checked into my hotel/room while the staff were being held at gunpoint.
In the 80s checking into your hotel/room was so much easier without all this technology nonsense.
I hope this cleared things up. Good luck with your english adventures!
You just arrived at a hotel. You can say any of these:
“You grab the bags, and I will go check in.”
“You grab the bags, and I will check in.”
“Should we check in before we go get dinner?”
“It is so late, what time do we have to check in by?”
If you need to say the hotel because it isn’t understood from the context you can say:
“You grab the bags, and I will go check into our hotel.”
Should we check in at the hotel before we go get dinner?"
Should we check into the hotel before we go get dinner?"
It is so late what time do we need to check into the hotel by?"
You cannot say, “I will check in hotel.” or “I will check in the hotel.”
You can say “I will check in at the hotel,” or “I will check in to the hotel.”
Check in is a noun phrase AND a phrasal verb, check into is just phrasal verb.
The difference in phrasal verbs is one can be separated and one can´t. I need to check in - inseparable. I need to check myself into the hotel - separable.
MacMillan Dictionary states that check in is an intransitive verb and check into is transitive.
Transitive means the verb can affect an object, for example “I kill him”. With transitive phrasal verbs you can create a pocket to put another word in, so with break down, we have “I will break the tent down and put it in a bag”, but break down is also an intransitive phrasal verb when it comes to meaning “stop working”, so “My car broke down”. Intransitive means it doesn´t affect an object but is more related to the subject, like “I die”. “I check in” “We need to check him into the hotel…”
That’s a typo or technically a grammatical error and should actually be “check in to.” To “check into” is to consider or evaluate in greater detail. “In to” and “into” are not the same, at least not at a level of understanding of English beyond the awareness of probably most native speakers.