Your custom commands can fail to save for many reasons:

• 1- Your custom command already exists or is a existing bot command.
• 2- The bot fails to recieve the JSON or guild, or the command name.
• 3- You exceed the custom command limit in your guild.

Your webhook will fail if the given webhook is invalid, or there was an error in the JSON given.

First, simply fill out the embed that you want, then press on the send button which is located at the bottom right of the page. Once clicked, you will have the option of sending it to a channel of your choice, click on one of these channels to send your embed.