Wordpress: PHP script cannot be find HTTP 404 ERROR - php

Question

My current mission is to create a complete theme on WordPress. And to this is, a login system. Now, i've created the form and everything looks just fine, the problem is that wordpress is brawling with me and cannot locate my signup script, it creates a HTTP 404 error. Now I think that this has something to do with wordpress permalink system because it wants to find a page, instead of my signup.inc.php script.
Now this frustrates me because im kind of new to coding and I have no idea how to fix it!
Here is my code linking to the actual file located in a folder called 'includes'
<form action='includes/signup.inc.php' method="post">
<div class="form-group">
<label for="Username">Username</label>
<input type="text" class="form-control" name="uid" id="uid" placeholder="Username" required>
<small id="userhelp" class="form-text text-muted">This name will show on forums and the socialpage.</small>
</div>
<div class="form-group">
<label for="firstname">Firstname</label>
<input type="text" class="form-control" name="firstname" id="firstn" placeholder="Firstname" required>
</div>
<div class="form-group">
<label for="lastname">Lastname</label>
<input type="text" class="form-control" name="lastname" id="lastn" placeholder="Lastname" required>
</div>
<div class="form-group">
<label for="email">Email Adress</label>
<input type="email" class="form-control" name="mail" id="inputemail" aria-describedby="emailHelp" placeholder="Email" required>
<small id="emailHelp" class="form-text text-muted">We'll never share your email with anyone else.</small>
</div>
<div class="form-group">
<label for="password">Password</label>
<input type="password" class="form-control" name="pwd" id="password" placeholder="Password" required>
</div>
<div class="form-group ">
<label for="password">Repeat password</label>
<input type="password" class="form-control" name="pwd-repeat" id="password" placeholder=" Repeat password" required>
<small id="passHelp" class="form-text text-muted">Please retype your password.</small>
</div>
<div class="form-group">
<div class="form-check">
<input class="form-check-input" type="checkbox" id="invalidCheck3" required>
<label class="form-check-label" for="invalidCheck3">Agree to terms and conditions</label>
<div class="invalid-feedback">
You must agree before submitting.
</div>
</div>
</div>
<button class="btn btn-dark" name="signup-submit" type="submit">Signup</button>
</form>

Answer 1

Please use this action in form:
<form action='<?php echo get_template_directory_uri(); ?>/includes/signup.inc.php' method="post">