This happens if the Android phone requires high accuracy to determine the location. Please follow these steps,
Press “Settings” option from phone -> "Security & Location" -> "Location" (under the Privacy sub-section) -> "Mode" -> then from the Location mode screen select "High accuracy"
1) Tap Settings option from phone
2) Tap Location option from Phone setting screen
3) Tap Mode option from Location Screen,
4) Now Select high accuracy mode than open Google Maps app and verify that the location is detect or not.
5) Try to operate Lock from Firstwatch app