Try the following solutions.
Check if Wi-Fi Direct (Simple AP) settings is enabled on the printer.
Check if the password for Wi-Fi Direct (Simple AP) connection has changed. You can check it on the printer's control panel (only available for specific model ) or network status sheet.
Check if the printer is turned off. If you have set the power off timer on the printer, the printer turns off automatically after a certain period of time.
For Android user, if you cannot connect to the printer from a smart device using Wi-Fi Direct connection even if the connection status is [Invited] on the smart device, the device may have been registered as a rejected device on the printer. Reset the registered information on the printer's control panel or Web Config. This function deletes all registered device information.