"Original form" of word is wrong (russian)

nominative singular form of фонтаны is фонтан but language reactor says it’s фонтана
(note: I’m not native so there is a chance I might be wrong, but I think it’s unlikely

my sources:

(see the declenations category) : фонтан - Wiktionary, the free dictionary

images:
Screenshot 2024-07-13 at 11.47.10 AM
Screenshot 2024-07-13 at 11.48.38 AM

I am Russian and want to tell you that you are right, the singular form is - фонтан