Is it an idiom: 'convert prospects into paying customers'?

[Julia]

Business English Lesson, Advanced Level

ESL/EFL Test #134 "Marketing Strategies", question 4

The primary goal of a such a strategy is to present sales staff with prospects to ......... into paying customers.

(a) connect
(b) connive
(c) convert
(d) convey

Business English Lesson, Advanced Level

ESL/EFL Test #134 "Marketing Strategies", answer 4

The primary goal of a such a strategy is to present sales staff with prospects to convert into paying customers.

Correct answer: (c) convert

Your answer was: incorrect
The primary goal of a such a strategy is to present sales staff with prospects to convey into paying customers.
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What does the word "convert" really mean in this sentence and why is it used this way?

Thank you
Julia

[Mister Micawber]

.
'Convert' means change-- change potential customers (prospects) into actual customers (paying customers).
.
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Native English teacher at Mister Micawber's