PHP get request resets page - php

Question

So, I'm making a PHP page. I'm trying to get a url like this
https://nikkiedev.com/folder/indexfile/?schedule-btn=true&time-zone=CET
but instead, when I click on my GET form for the time zone it goes to
https://nikkiedev.com/folder/indexfile/?time-zone=CET
Here's my code:
<div class='mobile-center'>
<form method="GET">
<button name="schedule-btn" type="submit" value="true" class="btn">schedule</button>
<button name="roles-btn" type="submit" value="true" class="btn">roles</button>
</form>
<?php
$sched_btn = $_GET["schedule-btn"];
$roles_btn = $_GET["roles-btn"];
if (isset($sched_btn)) {
echo "<div class='mobile-center'>";
echo "<h1>Change schedule</h1>";
echo "<hr>";
echo "<p>Choose time zone</p>";
echo "<form method='GET'>";
echo "<p>
<input type='radio' name='time-zone' value='CET'> CET
<input type='radio' name='time-zone' value='EST'> EST
<input type='submit'>
</p>";
echo "</form>";
$timezone = $_GET["time-zone"];
echo "</div>";
if ($timezone == "CET") {
echo "<h1>CET</h1>";
}
else if ($timezone == "EST") {
echo "<h1>EST</h1>";
}
}
?>
</div>

Answer 1

Add the value of $sched_btn as a hidden input in the new form.
if (isset($sched_btn)) {
echo "<div class='mobile-center'>";
echo "<h1>Change schedule</h1>";
echo "<hr>";
echo "<p>Choose time zone</p>";
echo "<form method='GET'>";
echo "<input type='hidden' name='schedule-btn' value='$sched_btn'>";
echo "<p>
<input type='radio' name='time-zone' value='CET'> CET
<input type='radio' name='time-zone' value='EST'> EST
<input type='submit'>
</p>";
echo "</form>";
$timezone = $_GET["time-zone"];
echo "</div>";
if ($timezone == "CET") {
echo "<h1>CET</h1>";
}
else if ($timezone == "EST") {
echo "<h1>EST</h1>";
}
}