Cannot connect IBS-P02R to M2 gateway

I’ve connected the M2 gateway to my wifi and added it to the Inkbird app. When I try to add the P02R as a sub-device, it adds to the app, but shows as ‘offline’ and doesn’t show on the M2. I’ve tried removing the batteries as mentioned in the manual. I don’t see any option to remove a device or sub—device in the app

Please access the settings of the IBS-M2 via the INKBIRD app. Please select the sensor you wish to disconnect and remove it.