Frames should be able to respond to user actions with an error message that will be displayed to the user. This enables frame developers a quick and easy way to give users feedback in response to input.

Proposed changes

A frame may respond to an action or transaction intent POST with an error response consisting of:

• 4XX status
• content-type: application/json header
• JSON body that contains a message property with a maximum of 90 characters

POST frame.server/action

400
content-type: application/json
{ message: "Invalid email" }

A Farcaster client must display the message to a user when a frame responds with an error response and allow the user to resubmit the same frame.