Got a "OnePlus A5000" error on iDevices

I have no problem installing apps on my iphones & ipads until recently. When I tried to install an app for pairing my watch recently, instead of going thru the "normals", it gave me a window asking to select a device but ..... the only option offered is "OnePlus A5000".  After selecting, it then asked to sign in to Google only to see a message that says "the app will be installed soon". But regardless how hard I try, I cannot find the app I wanted.  

Any idea what "OnePlus A5000" is? And......how can I solve this problem?

Thank you!