<form action="https://investr.pro/nl/calculation" target="my-iframe" method="post" id="iframe-form" style="visibility: hidden; height: 0;">
  <input type="hidden" name="api_key" value="7165ac094f5aae18882a6ebafc740af95bc9777cb0f295f5954ff1eee7d7d294">
  <input type="hidden" name="reference" value="[your_reference]">
  <input type="hidden" name="price" value="[your_price]">
  <input type="hidden" name="gross_rent_profit" value="[your_gross_rent_profit]">
  <input type="hidden" name="property_type_id" value="[your_property_type_id]">
  <input type="hidden" name="new_building" value="[your_new_building_boolean]">
  <input type="hidden" name="title" value="[your_title]">
  <input type="hidden" name="image" value="[your_image]">
  <input type="hidden" name="address_street" value="[your_street]">
  <input type="hidden" name="address_number" value="[your_number]">
  <input type="hidden" name="address_city" value="[your_city]">
  <input type="hidden" name="address_zip_code" value="[your_zip_code]">
  <input type="hidden" name="country_code" value="[your_country_code]">
  <input type="submit">
</form>

<iframe name="my-iframe" width="100%" height="1000px" frameborder="1" scrolling="yes"></iframe>

<script>
    (function() {
        var iframeForm = document.getElementById("iframe-form");
	iframeForm.submit();
    })();
</script>

test investr

exemple 2