Discord.Net/samples/InteractionFramework/Modules/MessageCommandModule.cs

using Discord;
using Discord.Interactions;
using Discord.WebSocket;
using System.Threading.Tasks;

namespace InteractionFramework.Modules
{
    // A transient module for executing commands. This module will NOT keep any information after the command is executed.
    internal class MessageCommandModule : InteractionModuleBase<SocketInteractionContext<SocketMessageCommand>>
    {
        // Pins a message in the channel it is in.
        [MessageCommand("pin")]
        public async Task PinMessageAsync(IMessage message)
        {
            // make a safety cast to check if the message is ISystem- or IUserMessage
            if (message is not IUserMessage userMessage)
                await RespondAsync(text: ":x: You cant pin system messages!");

            // if the pins in this channel are equal to or above 50, no more messages can be pinned.
            else if ((await Context.Channel.GetPinnedMessagesAsync()).Count >= 50)
                await RespondAsync(text: ":x: You cant pin any more messages, the max has already been reached in this channel!");

            else
            {
                await userMessage.PinAsync();
                await RespondAsync(":white_check_mark: Successfully pinned message!");
            }
        }
    }
}