"Why I can't I" or "why can I not"?

Question

Tell me please which one of the following sentences is correct.

Why can't I use this app, but I can use the other one.

Why can I not use this app, but I can use the other one.

I suspect that both sentence could be correct, if so, then which one is more formal?

Answer 1

Both sentences are fine. People speak differently I don't believe there's a difference besides the contraction.