"Sēteroti kostion vale ossȳngas."

Translation: The power of the magic spells frightens the man.

[ingochris]

"The magic spells's power frightens the man." is wrong, but there's no option for apostrophe with the preselected block words.

[StephieRice]

Spells'

No additional "s"

[potorgaret]

Shouldn't spells, as a noun, be counted as the same thing as magic spells?

[HinjakuHinjaku]

"A spells' power frightens a man" was marked incorrect. Why is it wrong?