Currently only 6 maps are supported for Payload mode:

• Angel City
• Black Water Canal
• Drydock
• Eden
• Exoplanet
• Forwardbase Kodai

The main issue when making maps support this mode is totally reliant on how much spawn points a map have towards its central area, as the vanilla game modes were designed to always spawn the players on the edges of the map and run to the battle that is happening in the middle, that is not the case for Payload since its more practical to spawn players closer to where the Nuke Titan is.

Eventually some more maps will be supported, but until there only these 6 will remain compatible.