Jua’alah is similar to Ijarah, however, it involved a fixed payment for a specific task that is not well-structured. An example of a Jua’alah would be offering a payment for finding a missing item. In a Jua’alah arrangement, the payment is made after the task has been completed.
According to a tradition in Al-Bukhari and Al-Muslim, the Prophet (SAW) approved of taking a sum as Jua’alah for blessing a sick person with the recitation of the Qur’an.
Source: Abdelhaleem, 6.