"Failed to send your message" — Not Server Issue

Hey there — thanks for clicking in and helping me out:

I am using the code below to collect some data from customers who wish to sell or find the value of their diamonds. For some reason, unbeknownst to me, the form does not submit and instead spits back a “Failed to send your message. Please try later or contact the administrator by another method” error.

I use Contact Form 7 on a number of other websites, all with the same host as this site so I am quite confused why this form doesn’t work and the rest do.

Any suggestions?

<table>
	<tr>
		<td style="padding:0 20px 0 0;">
			<p><strong>First Name</strong><span style="color:#006bcf;">*</span><br />[text* fn 30/]</p>
		</td>
		<td style="padding:0 20px 0 0;">
			<p><strong>Last Name</strong><span style="color:#006bcf;">*</span><br />[text* ln 30/]</p>
		</td>
		<td style="padding:0 20px 0 0;">
			<p><strong>Phone Number</strong><span style="color:#006bcf;">*</span><br />[tel* tel 30/]</p>
		</td>
		<td style="padding:0 20px 0 0;">
			<p>Email<br />[email email 30/]</p>
		</td>
	</tr>
</table>
<table>
	<tr>
		<td style="padding:0 40px 0 0; width:325px;">
			<p>Type of Diamond<br />[checkbox dt "Pear" "Princess" "Marquise" "Oval" "Radiant" "Emerald" "Heart" "Cushion" "Asscher"]</p>
		</td>
		<td style="padding:0 40px 0 0; width:130px;">
			<p>Approx Karat Weight<br />[text karat 15/]</p>
		</td>
		<td style="padding:0 20px 0 0;">
			<p>Certification<br />[checkbox ct "EGL" "GIA" "Other" "None"]</p>
		</td>
	</tr>
</table>
<table>
	<tr>
		<td style="padding:0 20px 0 0;">
			<p>Notes<br />[textarea notes 120x10]</p>
		</td>
	</tr>
</table>

	<p><strong>To submit your inquiry please answer the question below:</strong><span style="color:#006bcf;">*</span><br />[quiz Captcha "3+1=?|4"]</p>
	[submit]
<span style="margin-top:-30px !important; font-size:11px;">Information submitted will be treated with respect to your privacy and with maximum discretion.</span>

https://www.ads-software.com/plugins/contact-form-7/