They wanted a sign that would prove that Jesus' power and authority were from God. Possible meanings are 1) The word "heaven" is a metonym for God. AT: "a sign from God" or 2) the word "heaven" refers to the sky. AT: "a sign from the sky" (See: [[rc://en/ta/man/translate/figs-metonymy]])
The Pharisees tried to test Jesus to make him prove that he was from God. Some information can be made explicit. AT: "to prove that God had sent him" (See: [[rc://en/ta/man/translate/figs-explicit]])