en_tn_lite_do_not_use/act/25/03.md

asked him for a favor

Here the word "him" refers to Festus.

that Festus might summon Paul to Jerusalem

This means that Festus would order his soldiers to bring Paul to Jerusalem. Alternate translation: "that he might order his soldiers to bring Paul to Jerusalem"

so that they could kill him along the way

They were going to ambush Paul.