How can I add hd quality ads?

Hello, I am having troubles with uploading hd quality ads. It tells me that the dimensions aren’t correct, but when I upload the same ad but low quality it uploads perfectly fine, but it looks horrible in low quality. Also the ad is not made by me, I payed someone to make it.

Can someone help me with this?

Try to contact the person. If the person couldn’t do it, try to get your money back from the person.