The captcha image is not showing up in 4.0.21

the captcha image didn’t show at all. I currently using the 4.0.21.

Checking the code I found this:

<div id="fscf_captcha_image_div1" style="width:250px; height:65px; padding-top:2px;">

<img id="fscf_captcha_image1" width="175" height="60" title="Security code to prove you are human." alt="Security code to prove you are human." src="https://skyhawkttc.com.au/wp-content/plugins/si-contact-form/captcha/securimage_show.php?prefix=CJHyQCOadHJOKo7z" style="border-style:none; margin:0; padding:0px; padding-right:5px; float:left;"></img>
<input id="fscf_captcha_prefix1" type="hidden" value="CJHyQCOadHJOKo7z" name="fscf_captcha_prefix1"></input>
<div id="fscf_captcha_refresh1"></div>

</div>

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Please have a look at https://skyhawkttc.com.au/contact-us/
and advise how to solve this issue. Thank you and best regards. Henry.

https://www.ads-software.com/plugins/si-contact-form/