Discord servers are enforcing a rule that bots cannot access Message Content without declaring a Privileged Intent. https://support-dev.discord.com/hc/en-us/articles/4404772028055
Bots in fewer than 75 (ie most bots) will need to check a box in the developer docs. Bots in >75 serves will need to be verified to have access to these intents.
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Click on the application you want to authorize
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In the taskbar on the left, select the 'Bot' tab
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Scroll down to "Privileged Gateway Intents"
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Enable Presence, Server Members, and Message Content intents.