“Register in” works when talking about the act of registering for something. It’s a fairly common preposition that we can use after “register” to show that we want to sign up for somethi… See more

“Register in” works well when referring to the act of registration. This is more in line with the verb rules we use in many cases. It makes sense for us to use this because it shows that … See more

“Register at” is more specific. We use it to refer to signing up at a specific place or time. It works when we have been told that a specific thing needs to happen when we register. Fo… See more

“Register in” and “register at” are not interchangeable. We use “in” to refer to a thing that we are signing up for. It refers to the act of registration before anything else. “At” works … See more

According to Google Ngram Viewer, “register in” is more popular. This is because it’s more general, meaning that it often refers to more situations. We use it in many mor… See more