Contact Form throwing error

I have GMail SMTP installed. On the contact form here-https://dbkpainting.com/request-an-estimate/, when I submit info, it throws an “Error 500”, but the info is recorded in the feedback section of the site, but the emails are not set to the email specified in the form.

It was working about a month ago, and nothing has changed. I realize this may be out of the WPMU realm, but I hope you can help. Thanks

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