From IOS 13 onwards, when you install the app and activate geolocation a system message asking for permission to allow location services to be used will appear. Select the option to "Allow when App is in use".
Shortly after when the App tries to use the location services when the app is closed, another system message will pop up asking if you want to allow location services use at all times. This option should then be selected.
If any concerns. check the App permissions in the IOS App settings.