Great.
I should have started with this. Would have saved an hour. 
Get the response where you see 500.
Click on the emailsending.php line item. Then you will see the other set of headers… select response there.
{“code”:1,“file”:"/home/customer/www/1connect1.com/public_html/dmxConnectLib/PHPMailer/PHPMailer/PHPMailer.php",“line”:3551,“message”:“Could not access file: /includes/EmailCampaign//imagePr/Email/155/Carpet Cleaning Repairs.JPG”,“trace”:"#0 /home/customer/www/1connect1.com/public_html/dmxConnectLib/PHPMailer/PHPMailer/PHPMailer.php(4092): PHPMailer\PHPMailer\PHPMailer->addEmbeddedImage(’/includes/Email…’, ‘697b934e76fcf69…’, ‘Carpet Cleaning…’, ‘base64’, ‘image/jpeg’)\n#1 /home/customer/www/1connect1.com/public_html/dmxConnectLib/modules/mail.php(110): PHPMailer\PHPMailer\PHPMailer->msgHTML(’<base href="/in…’, ‘/includes/Email…’)\n#2 /home/customer/www/1connect1.com/public_html/dmxConnectLib/lib/App.php(193): modules\mail->send(Object(stdClass), ‘’)\n#3 /home/customer/www/1connect1.com/public_html/dmxConnectLib/lib/App.php(157): lib\App->execSteps(Object(stdClass))\n#4 /home/customer/www/1connect1.com/public_html/dmxConnectLib/lib/App.php(127): lib\App->execSteps(Array)\n#5 /home/customer/www/1connect1.com/public_html/dmxConnectLib/lib/App.php(116): lib\App->exec(Object(stdClass), false)\n#6 /home/customer/www/1connect1.com/public_html/dmxConnectLib/lib/App.php(94): lib\App->exec(Object(stdClass))\n#7 /home/customer/www/1connect1.com/public_html/dmxConnect/api/Security/EmailCamp/EmailSending.php(8): lib\App->define(Object(stdClass))\n#8 {main}"}
There you go. That's your error. In your HTML, somewhere you have a link to an IMAGE, and Wappler is unable to find it.
This image, I assume is coming from summernote image upload. You need to fix the image path here.
I haven't used this yet, so don't know how summernote image upload works.
Assuming is bad. But I was assuming the email will find it because It was easily display on the page before It was sent.
Thank you for helping find the issue. I guess I will have to browser between all summernote previous question to see if someone did it before.