That could be why, you cannot send tables to Discord to post in an embed, strings only.
You’ll need to either delete that field or use JSONEncode to change the table to a string (essentially).
The max amount of characters you can have in a field value is 1024, and if you exceed that, or in your case provide a non-string, you will get 400 Bad Request.
Discord’s docs on embeds: Discord Developer Portal
Discord embed limitations: Discord Developer Portal