add friend system in php - php

Question

I am trying to build a friend system in php I have the tables, database and the logic in place. I am having trouble getting the friend request receiver's id.
I have registeredusers friends updates table. The registeredusers table looks like this,
CREATE TABLE `registeredusers` (
`id` int(11) NOT NULL,
`FirstName` varchar(50) NOT NULL,
`LastName` varchar(50) NOT NULL,
`UserName` varchar(50) NOT NULL,
`Email` varchar(50) NOT NULL,
`Password` varchar(255) NOT NULL,
`ResetPassword` int(7) DEFAULT NULL,
`friends` int(255) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
friends
CREATE TABLE `friends` (
`friend_one` int(11) NOT NULL,
`friend_two` int(11) NOT NULL,
`status` enum('0','1','2') DEFAULT '0'
) ENGINE=InnoDB DEFAULT CHARSET=latin1;
The requester's ID would be INSERTED into friend_two and receiver's ID would get into friend_one. here's my code
<?php
include 'dbh.php';
$sql = "SELECT * FROM registeredusers";
$result = mysqli_query($connection,$sql);
$row = mysqli_fetch_assoc($result);
$username = $row['UserName'];
$requesterU = $_GET['user'];
echo "the requester is ".$requesterU;
while($row=mysqli_fetch_array($result)){
$id = $row[0];
$username = $row[1];
echo "
<form action='list of users.php'>
$id $username<input type='submit' value='send request' name='friendsbanalo'></input></form>";
}
$sql = "SELECT * FROM registeredusers WHERE UserName = '$requesterU'";
$result = mysqli_query($connection,$sql);
$row = mysqli_fetch_assoc($result);
$requester_id = $row['id'];
echo "requester's id ".$requester_id;
if(isset($_POST['friendsbanalo'])){
$sql = "INSERT INTO friends (friend_one,friend_two) VALUES('$requester_id','$reciver_userid')";
$result = mysqli_query($connection, $sql);
}else{
echo "error";
}
?>
I am not able to get the receiver's ID, can anyone tell me how can I get receiver's ID? I tried searching for the solution and the answers were too complicated for me to understand. I tried (on a separate file) INNER JOIN but I couldn't get it to work.