RoR - Capsens/universign - SignatureField - The coordinates aren't working

I'm trying to set a transaction to Universign with the "capsens_universign" gem.

Here's my code to create the transaction:

document_from_content = Universign::Document.new(
        name:    'another.pdf',
        content: File.open("tmp/test.pdf").read
    )

    signer = Universign::TransactionSigner.new(
        first_name:   "Signer's first name",
        last_name:    "Signer's last name",
        email:        'test@gmail.com',
        phone_number: 'SOME_PHONE_NUMBER',
        success_url:  'https://my_app.com',
        signature:    Universign::SignatureField.new(coordinate: [37,684], page: 5)
    )

    transaction = Universign::Transaction.create(
        documents: [document_from_content],
        signers:   [signer],
        options:   { profile: 'default', final_doc_sent: false, handwritten_signature_mode: 0}
    )

I got a code 200 response from this. I can sign the pdf BUT signature stamps are not showing in the PDF generated by Universign when the transaction is completed.

Is it because of this configuration ? Or maybe I didn't understand well the different signatures configurations.