Which one is correct?
1. When I arrived, I wanted to pay the fare but realized I didn’t have
any money because I had left my wallet at home.
2. 1. When I arrived, I wanted to pay the fare but I found out that I
didn’t have any money because I had left my wallet at home.
The first one is correct.
"Realized" is more for when you became aware of something yourself, more internal
"Found out" is more for when you discovered something externally, usually through someone else telling you, it's like new information