WPS was a common method of adding a device with a limited user interface (printers, IoT devices) to a wireless network.
Plume does not currently support enabling WPS in the app, as it was discovered to be a less secure connection method for Wi-Fi networks.
Check with your device manufacturer, as many devices have an alternative method to connect them to your network that is not dependent on WPS. If your device only has the ability to connect to Wi-Fi using WPS, contact Plume Support by phone or chat for assistance connecting that device.