In Brazil, and only in Brazil, precisar (to need) drops the "de" when followed by a verb, but in European Portuguese which is followed by all the other Portuguese speaking countries and areas, the preposition is retained with the following verbs too:
I think if you click on the link I had enclosed in my previous comment you will find several examples along with an extensive discussion (in Portuguese as a bonus) that explains even better than I could.
But it is interesting to me indeed that you always include the preposition in Brazil. Thank you for sharing that. From my understanding there are pockets in Brazil where the Portuguese is closer to that of Portugal. And perhaps also for first generation Brazilians with Portuguese parents too. :)
EDIT: 05/19 – I have since discovered that there are several areas in Brazil that do use the preposition with precisar + infinitive.
What this means is Duo should always accept the preposition with precisar and if not, then report.
Also (to add to Alyssontlb's answer), My father likes sleep in the construction of your sentence, the sleep functions as a noun (rather than a verb as in the Duo exercise) which would then be, [o] sono in Portuguese.