header with german coding

I want to address a form on a page. Everything is up and running except the validation. I send you few remarks which are strange for me:

1. Head - section

<meta name="generator" content="WordPress 4.7.3" />
<link rel="canonical" href="http://huppenbroich.de/ris/einstellung-bekanntgeben/" />
<link rel='shortlink' href='http://huppenbroich.de/ris/?p=537' />
<link rel="alternate" type="application/json+oembed" href="http://huppenbroich.de/ris/wp-json/oembed/1.0/embed?url=http%3A%2F%2Fhuppenbroich.de%2Fris%2Feinstellung-bekanntgeben%2F" />
<link rel="alternate" type="text/xml+oembed" href="http://huppenbroich.de/ris/wp-json/oembed/1.0/embed?url=http%3A%2F%2Fhuppenbroich.de%2Fris%2Feinstellung-bekanntgeben%2F&format=xml" />
<script scr=http://huppenbroich.de/ris/wp-content/themes/generatepress_child/datum.js>

The coging of two links is very strange. What may be the reason?
I added the script unsing hook wp_head.

2. In Firefox's browser console I found the following message:

ReferenceError: form_validation is not defined

In the page with the form is as follows:

<script src="http://huppenbroich.de/ris/wp-content/themes/generatepress-child/datum.js"></script>
<!-- [wpforms id="533"] -->
<p>
<div class="wpforms-container wpforms-container-full" id="wpforms-533">
<form method="post" enctype="multipart/form-data" id="wpforms-form-533" onsubmit="return form_validation()" action="../sende-details.php" class="wpforms-validate wpforms-form" data-formid="533">

And this is the schript:

`
<script type="text/javascript">
function form_validation() {
var arr = document.forms['sende-details']['Datum'].value.split('.');
if (arr[0] <= 31 && arr[1] <= 12 && arr[2] >= 2017) {
alert('Alles klar!');
} else {
alert('Datum ungültig!');
}
}
</script>

Where is the error????

Appreciate any help!