Contact form file attachment is not working

I have tried everything but sadly nothing worked. I have read all articles, yet nothing works. After creating my form https://nhbschool.com/request-membership/ I found that the form delivers to my mail but unfortunately doesn’t have the attached documents> Below are my codes:
For the form:
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Fill and submit certificates earned or send attached certificate earned via email to [email protected]
<label> Your Full Name (required)
[text* your-name] </label>

<label> Your Email (required)
[email* your-email] </label>

<label> Tel number [tel tel-453] </label>

<label> Upload Certificate of Completion [file certificate1 filetypes:pdf|gif|png|jpg|jpeg|txt ]</label>
<label> Upload Certificate of Completion [file certificate2 filetypes:pdf|gif|png|jpg|jpeg|txt ]</label>
<label> Upload Certificate of Completion [file certificate3 filetypes:pdf|gif|png|jpg|jpeg|txt ]</label>
<label> Upload Certificate of Completion [file certificate4 filetypes:pdf|gif|png|jpg|jpeg|txt ]</label>
<label> Upload Certificate of Completion [file certificate5 filetypes:pdf|gif|png|jpg|jpeg|txt ]</label>

[submit “Send”]
Fill and submit certificates earned or send attached certificate earned via email to [email protected]
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For the mail
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email tags placed in file attachment:
[certificate1][certificate2][certificate3][certificate4][certificate5]