What information should I include when asking for help with a 'custom payload error' online (e.g., on Reddit or a forum)?

When seeking help online, provide as much detail as possible. Include the Minecraft version, the server software (Forge, Fabric, Vanilla), a complete list of installed mods (with versions), the full error message from the server logs, and a description of what you were doing in the game when the error occurred. Include any recent changes made to the server or mod list. Also, specify if the issue is reproducible or intermittent.