1. Revelation 18:6 (ESV)
  2. Exposition

Who gives the instruction to “pay her back”?

Revelation 18:6 (ESV)

6 Pay her back as she herself has paid back others, and repay her double for her deeds; mix a double portion for her in the cup she mixed.

The verb pay back is clearly a command, and in Greek it is in the plural: You all, pay her back! The one who gives the command is still the voice from heaven (Revelation 18:4) and so the command comes with God-given authority.