Official rule text
21.5 Players can trade commodities following the rules for 23.2 TOKENS: Tokens are limited to those included in the game, transactions. When a player receives a commodity from except for the following: another player, the player who received that token converts it into a trade good by placing it in the trade good area of their • Control Tokens • Trade Good Tokens command sheet with the trade good side faceup. • Fighter Tokens • Infantry Tokens a That token is no longer a commodity token; it is a trade
View official source
Source: Twilight Imperium: Fourth Edition - Living Rules Reference: Prophecy of Kings
Expansion: Prophecy of Kings
Version: 2.0
Reference: Rule 21.5