No, no one paid the US to get it to participate in World War II.
First of all, think about what got the US into the war. The US did not enter the war until it was forced to do so when Japan attacked the US naval base at Pearl Harbor. If the French and British had bought US involvement, it would have gotten in before then.
Second, remember that the US was already spending a lot of money helping the Allies before it entered the war. The US was sending millions of dollars worth of equipment to the Allies via Lend-Lease.
So, there is no question of the US having entered the war in return for any sort of financial considerations.