If I use King's Edict do I have to pay Deflect on the unit I choose?

No, you do not have to pay the Deflect cost when using King's Edict.

According to RiftJudge FAQ #509 and FAQ #8616, King's Edict does not target. The spell instructs players to make a choice during its resolution, rather than the spell itself choosing a target when it is placed on the chain.

Because the spell does not "choose" a unit as a target, the Deflect keyword—which specifically triggers when a spell or ability "chooses" a permanent—does not apply.

Summary of the interaction:

• King's Edict is played and placed on the chain.
• Because it does not target, no Deflect costs are paid at this time.
• Upon resolution, each opponent is instructed to choose a unit they control (or a unit you don't control, depending on the specific wording/FAQ interpretation for your format).
• Since the choice is made by the players during resolution, Deflect is not triggered.