Impossibility of object

The impossibility of the object of a contract may be:
Physical, or when the thing or service in the very nature of things cannot exist (e.g., a dog that can fly) or be performed. Moreover, when we talk of services, the impossibility may be:
    a) Absolute, or when the act cannot be done in any case so that nobody can perform it; or
    b) Relative, or when it arises from the special circumstances of the case (e.g., to make payment to a dead person, to drive a car on flooded highways, etc.) or the special conditions or qualifications of the obligor (to paint a portrait by a blind person, etc.).[1][2]

Legal, or when the thing or service is contrary to law, morals, good customs, public order, or public policy.

[1] Articles 1266 and 1267, Civil Code.

[2] De Leon. (2014). Obligations and Contracts.