Message are sent to administrator, but not for customer

Hello,
I have a form in https://quatroestacoes.roov.com.br/
After submission, the system should send a notification to the admin and a confirmation message to the person who sent the form. However, only the message to the admin is being sent. I've already tried adjusting the SMTP settings, using the domain's email server, and also Amazon SES. In both cases it happens the same way.

Any idea?

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