Custom emojis are only available for bots that have paid a username, such as @wallet.
For more information, please refer to this link: https://fragment.com/about#q-can-i-assign-my-upgraded-username-to-a-different-bot
If you have already purchased a username for your bot, you can send emojis using the following syntax:
<tg-emoji emoji-id=“5368324170671202286”>👍</tg-emoji>