An electronic device displays a messaging user interface of a messaging application on the display, the messaging user interface including a conversation transcript of a messaging session between a user of the electronic device and at least one other user, a first message-input area, and a launch icon for an interactive application. While displaying the messaging user interface, the device detects an input that activates the launch icon for the interactive application. In response to detecting the input that activates the launch icon for the interactive application, the device displays a user interface for the interactive application, the interactive application user interface including a second message-input area that is distinct from the first message-input area. While displaying the interactive application user interface, the device detects input of a first message in the second message-input area. In response to detecting the input of the first message in the second message-input area, the device displays the first message in the second message-input area. While displaying the first message in the second message-input area, the device detects an input that corresponds to a request to post the contents of the second message-input area to the messaging session; and, in response to detecting the input that corresponds to the request to post the contents of the second message-input area to the messaging session, the device transmits the first message to one or more electronic devices that correspond to the at least one other user included in the messaging session, wherein the one or more electronic devices display the first message in a conversation transcript corresponding to the messaging session.