Discord.Net/docs/faq/client-basics.md

# Client Basics Questions

## My client keeps returning 401 upon logging in!

> [!WARNING]
> Userbot/selfbot (logging in with a user token) is not 
> officially supported with this library.
>
> Logging in under a user account may result in account 
> termination!

There are few possible reasons why this may occur.
	1. You are not using the appropriate [TokenType]. 
	If you are using a bot account created from the Discord Developer 
	portal, you should be using `TokenType.Bot`. 
	2. You are not using the correct login credentials. 
	Please keep in mind that tokens start with `Mj*`. 
	If it starts with any other characters, chances are, you might be 
	using the *client secret*, which has nothing to do with the login 
	token.

[TokenType]: xref:Discord.TokenType

## How do I do X, Y, Z when my bot connects/logs on? Why do I get a `NullReferenceException` upon calling any client methods after connect?

Your bot should **not** attempt to interact in any way with 
guilds/servers until the [Ready] event fires. When the bot 
connects, it first has to download guild information from 
Discord in order for you to get access to any server 
information; the client is not ready at this point. 
 
Technically, the [GuildAvailable] event fires once the data for a 
particular guild has downloaded; however, it's best to wait for all 
guilds to be downloaded. Once all downloads are complete, the [Ready] 
event is triggered, then you can proceed to do whatever you like.

[Ready]: xref:Discord.WebSocket.DiscordSocketClient.Ready
[GuildAvailable]: xref:Discord.WebSocket.BaseSocketClient.GuildAvailable

## How do I get a message's previous content when that message is edited?

If you need to do anything with messages (e.g. checking Reactions, 
checking the content of edited/deleted messages), you must set the 
[MessageCacheSize] in your [DiscordSocketConfig] settings in order to 
use the cached message entity. Read more about it [here](../guides/concepts/events.md#cacheable).
1. Message Cache must be enabled.
2. Hook the MessageUpdated event. This event provides a *before* and 
*after* object.
3. Only messages received *after* the bot comes online will be 
available in the cache.

[MessageCacheSize]: xref:Discord.WebSocket.DiscordSocketConfig.MessageCacheSize
[DiscordSocketConfig]: xref:Discord.WebSocket.DiscordSocketConfig
[MessageUpdated]: xref:Discord.WebSocket.BaseSocketClient.MessageUpdated