Official rule text
93.3 A player can spend trade goods at any time during the game. spending one command token from their strategy pool and four resources. 93.4 A player can spend a trade good in one of the following ways: RELATED TOPICS: Initiative Order, Resources, Strategic Action, a In place of spending one resource.
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Source: Twilight Imperium: Fourth Edition - Living Rules Reference: Prophecy of Kings
Expansion: Prophecy of Kings
Version: 2.0
Reference: Rule 93.3