What does "entails of the details" mean?

[Baubau]

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #634 "Prepositional Phrases - On, In, Under and Out (8)", question 3

You need to get that agreement ......... paper. A verbal agreement is not enough in this case. You have to get him to sign a contract that entails of the details you talked to him about beforehand.

(a) on
(b) in
(c) under
(d) out

English Language Proficiency Tests, Advanced Level

ESL/EFL Test #634 "Prepositional Phrases - On, In, Under and Out (8)", answer 3

You need to get that agreement on paper. A verbal agreement is not enough in this case. You have to get him to sign a contract that entails of the details you talked to him about beforehand.

Correct answer: (a) on

Your answer was: correct
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Hello,
I can't understand what "entails of the details" means, could someone please rephrase or explain it?
Thanks in advance.

[Kitosdad]

Simply to explain what was discussed or agreed to.
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Keep it simple ... Keep it interesting.