Since InfinityFree is a very popular free hosting, it needed to enforce some limits to block bad bots and hackers. However, this system is also blocking some good bots like the LE bots, and therefore you cannot get such a certificate there.
However, @Ranakhas found a workaround:
Since we saw that new users were still having a hard time using it, we created this video in case anyone has trouble following that guide.
We hope this works for you!