E_DEPRECATED: strstr(): error

Hi All,

I've got an error that I’m not sure how to fix.

Any thoughts?

Here’s the error:

#1883 - E_DEPRECATED: strstr(): Non-string needles will be interpreted as strings in the future. Use an explicit chr() call to preserve the current behavior
/home2/nawaflco/public_html/nawafl/newslettersdetail.php (line 408)
https://nawafl.org/newslettersdetail.php

And here’s the offending code:
<?php foreach ($newsletter_announcementsRecords as $record): ?>
<?php $availabledates3 = join(', ', $record['newsletter_date:values']) ?>
<?php if (strstr($availabledates3, $newsletter_templateRecord['newsletter_date'])): ?>
<table align="center">
<tr>
<td colspan="3" align="left" valign="top" ><hr color="#<?php echo $nawa_colorsRecord['menu_background_color'] ?>" width="300" />
<div style="background-color:#<?php echo $newsletter_templateRecord['announcements_title_box_background_color'] ?>; padding:10px;" <?php if($newsletter_templateRecord['announcements_rounded_corners']==1):?>class="round-corner-3" <?php endif ?>>
<div align="center" style="background-color:#<?php echo $newsletter_templateRecord['announcements_title_background_color'] ?>; padding:10px;" <?php if($newsletter_templateRecord['announcements_rounded_corners']==1):?>class="round-corner-3" <?php endif ?>> <span class="heading_font"><?php echo $newsletter_templateRecord['announcements_main_title'] ?></span></div>
</div></td>
</tr>
</table>
<?php break ?>
<?php endif ?>
<?php endforeach; ?>

Thanks,

Jerry Kornbluth