Form - Array To String Conversion Error

"An exception has been thrown during the rendering of a template ("Array to string conversion")."

---
title: Contact
form:
    name: contact
    fields:

        location:
            type: select
            label: 'Select your city'
            multiple: false
            options:
                test1:
                    value: 'test1'
                test2:
                    value: 'test2'
                test3:
                    value: 'test3'
                    disabled: true
            validate:
                required: true
                message: 'Select your city'

    buttons:
        submit:
            type: submit
            value: Send
        reset:
            type: reset
            value: Reset

    process:
        email:
            subject: '[Contact form] {{ form.value.name|e }}'
            body: '{% include ''forms/data.html.twig'' %}'
        save:
            fileprefix: contact-
            dateformat: Ymd-His-u
            extension: txt
            body: '{% include ''forms/data.txt.twig'' %}'
        message: 'Thank you for your message!'
        display: thankyou

process:
    markdown: true
    twig: true
---