and my function to get the distance is

fun distanceBetween(cord1: Coordinates, cord2: Coordinates): Double {
    val (lat1deg, lon1deg) = cord1
    val (lat2deg, lon2deg) = cord2

    val r = 6371e3; // metres
    val lat1 = lat1deg.toRadians()
    val lat2 = lat2deg.toRadians()
    val deltaLat = (lat2deg - lat1deg).toRadians()
    val deltaLon = (lon2deg - lon1deg).toRadians()

    val a = sin(deltaLat / 2).pow(2) +
            cos(lat1) * cos(lat2) * sin(deltaLon / 2).pow(2)
    val c = 2 * atan2(sqrt(a), sqrt(1 - a))

    return r * c;
}

You could look at https://spring.io/blog/2016/03/20/a-geospatial-messenger-with-kotlin-spring-boot-and-postgresql as an example of how to work with geospatial data.