This may happen if you have location access turned off or have previously rejected a request by the app for permission to access your location.
The plotaroute app will need location permissions for both the host browser (Chrome or Safari) and the plotaroute website. You can check these location permissions as follows.
Safari - Under iPhone Settings select Privacy, Location Services, Safari - check that Location Access is enabled and that Precise Location is turned on.
Plotaroute - Go to www.plotaroute.com in Safari, click the AA icon in the address bar, select Website Settings and check that the Location setting is either Ask or Allow.
Chrome - Under your device Settings select Location, App permission and check that Chrome is not denied location access.
Plotaroute - Go to plotaroute.com in Chrome, click the menu icon in the top right, select Settings then Site Settings and Location and check that the Location switch is on and that plotaroute.com is not listed as blocked.