Form doesn't recognize [ method="post" ]

Hi!

I'm trying to create a contact form in a website (in WordPress) but it never worked, not matter what I did. The thing is, I went to the basics and made a super simple form to test it:

<form>
        <input type="text">
        <input type="submit" value="Enviar">
</form>

I tested in two websites, the one I want to add the contact form (I'm going to call it Site A), and another that I'm just starting (Site B).

I noticed that if I submit this form if both Sites, the URL appears like this: http://site.com/contact/? (with the '?' at the end). And when I added the [method="post"] like this:

<form method="post">
        <input type="text">
        <input type="submit" value="Enviar">
</form>

In Site B the URL appeared without the '?' like this: http://site.com/contact

But in Site A continues to have the '?'... so I assume that in Site A the form is not recognizing the [method="post"] and I don't know why. Can anyone help me, please?

Because this problem is also making WordPress plugins (of contact form) don't work.

Thanks!