I want a clean URL but i cannot GET string on the other page. I am using preg_replace to remove spaces with -

Question

i want to send id and post caption through my page to the post page. When i try to GET id only, it works but when i try to get caption it does not work. can someone please help? It's been many days but cannnot get rid of this error. Thank you

.htaccess-rule

RewriteRule ^post/([0-9]+)/([0-9a-zA-Z]+)$ post.php?id=$1&cap=$2 [QSA,L]

Sending it from list page

$cp = preg_replace('/[^A-Za-z0-9\-]+/', '-', $row['caption']);
$cpnew = str_replace(" ", "-", $cp);
<?php echo "<a href='post/$id/$cpnew'>"; ?>

Getting on post page

$cap ="". preg_replace('^[\x{0590}-\x{05fe} ]+', '', $_GET['cap']);
$capnew = str_replace("-", " ", $cap);