How to send a form using the POST method and follow the link?

Question

PHP

Tell me please! The situation is as follows. When you click on the button, a modal window opens, a form is filled in the window (Name, number, mail), when you click on the "send application" button, you need to send the XML code and follow the link to fill out the questionnaire. I attached the code below and here is a link to the instruction provided by the bank - https://dropmefiles.com/iplUJ
This is the first time I've come across it, and please tell me the literature in order to solve such issues myself in the future.
Thanks in advance to everyone who responds!

<form action="https://anketa.alfabank.ru/alfaform-pos/endpoint" method="post" enctype="application/x-www-form-urlencoded">
<textarea name="InXML" >
<inParams>
<companyInfo>
<inn>1111111111</inn>
</companyInfo>
<creditInfo>
<reference>A0000000001</reference>
</creditInfo>
<clientInfo>
<lastname>Иванов</lastname>
<firstname>Иван</firstname>
<email>[email protected]</email>
<mobphone>9876543210</mobphone>
</clientInfo>
<specificationList>
<specificationListRow>
<category>CRT_TV</category>
<code>#123</code>
<description>Samsung</description>
<amount>1</amount>
<price>10000</price>
</specificationListRow>
<specificationListRow>
<category>MOBILE_PHONE</category>
<code>#1222</code>
<description>HTC</description>
<amount>2</amount>
<price>10000</price>
<image>http://www.photo.ru/product.png</image>
</specificationListRow>
</specificationList>
</inParams>
<br>
</textarea>
<input type="submit" value="Купить в кредит" style="float: left;">
</form>

Answer 1

Probably include javascript. Or, if you want to go to the page where the form is being validated, then use the action tag on the form.