Use the ToastMessage component for messages and actions that should be helpful but ultimately ignorable without any impact on what the user wants to get done.
When to use each variation
Toast with a title
For when you want to just provide a quick process update like a confirmation
Connected to dapp
Toast with a subtitle
For when you want to provide more value through extra helpful information. Ask yourself when implementing your toast: is there anything else I could tell the user that would be useful?
You have 4.20 ETH remaining
This might take a few minutes
You didn't have enough Ether
How it works
ToastMessage component disappears automatically
Users can dismiss them manually
They display one at a time, so if multiple messages are necessary, each one should appear after the previous message.
Use for non-critical information
Don't use toast messages for information that will directly impact the success of completing a task, for example a network failure. They dismiss automatically so things can be missed easily. Note: users are able to dismiss them immediately manually. For critical information, use Modal to bring that info to the user's attention.
Switch to Rinkeby to start the transaction
Think about placement
Toasts should steer clear of navigational elements and important areas of the screen. Consider that the MetaMask browser extension could potentially hide your toast messages.
Stick to one optional link
This link should support your update and must be optional. This might be to provide further information (like linking to Etherscan) or something that can affect the process (like cancelling while your payment is in a processing state). Link copy should ideally be verb-led like "Check", "View", "Buy" or "Change".