What is the ruling of Islamic law on receiving a salary from a job that involves two parts: one performed correctly, and the other based on fictitious and unrealistic field reports?

As long as on-site presence is a condition for receiving monthly dues, these dues are not entirely permissible unless this condition is met. Deception and fraud are not allowed to circumvent this condition, due to the Almighty’s saying: "O you who have believed, fulfill [all] contracts," and due to the Prophet's (peace be upon him) saying: "Muslims are bound by their conditions."