That is pretty normal for credit card companies to have catches, especially the zero percent interest cards. If you are late on a payment, the zero percent goes to like 28% interest. If you go over, they have over limit fees.
You have to read the fine print... that it how they make money when you don't follow the fine print to a T.
If you miss a payment, tell them you were in the hospital!
I had a Chase card that was Zero Percent purchases but due to a mixup on another card that was supposed to be canceled, they canceled the wrong card. So when I got it straighted out, I got a new card and it was only Zero Percent balance transfer and I was not aware of it. I did not have the original information to prove that I originally applied for a Zero Percent purchase card.
Anyway, I put a new John Deere 4-Wheel Steer yard tractor on it and then noticed I was getting charged interest. So I paid it off because I didn't want to pay the interest. Well they tried to charge me more interest the following month for the time it was on the previous month and I was mad and flat out told them I AM NOT PAYING IT. So they took the interest off. LOL