You get what you pay for when using a cheap FHP belt for a job like this.
Correct belt has a 32º cross-section, an "A" belt has 40º cross-section.
NO WAY will the cheap replacement work as well, or last as long.
PLUS, this belt has a tough job... is is also used as the tractor's clutch. Needs to grab and release properly for safe operation by the trator, not to mention by a kid!