Form action WordPress Plugin

Question

I am creating a specialized WordPress plugin, and its not for use outside of this singular case for the rest of the question we will refer to the wordpress plugin folder as plug-folder. Inside the plug-folder I have multiple files, a file named form_submit.php and a file named form_template.php. form_template.php is registered as a page template that can be applied to any post or page through the WordPress dashboard. The issue is because the form_submit.php file is inside the plugin folder how do I map my form action to post the data to the file? Simply listing it as

<form action="form_submit.php" method="post" >

Will not work as I need because it will be looking for the form_submit.php in the root directory of the site not the plugin folder and trying to map out the URL scheme for it in the plugin folder like

<form action="wp-content/plugins/plug-folder/form_submit.php" method="post" >

Doesn't work either, does a method exist that I am not thinking of?

Edit: After switching to use plugins_url() as suggested its working in one of the two instances where I am using forms. My register form (attached below) is not working, comes back error loading page.

<form action="<?php echo plugins_url( 'register_submit.php', __FILE__ ); ?>" method="post" autocomplete="off">

                            <?php if($_GET['error'] == 'username'){ ?>
                                <div class="error_message">
                                    Uh oh! That username is already taken.
                                </div>
                            <?php }else if($_GET['error'] == 'email'){ ?>
                                <div class="error_message">
                                    Uh oh! That email is already in use.
                                </div>
                            <?php }else if($_GET['error'] == 'email_invalid'){ ?>
                                <div class="error_message">
                                    Uh oh! Make sure to enter a valid email.
                                </div>
                            <?php }else if($_GET['error'] == 'signup_blank'){ ?>
                                <div class="error_message">
                                    Uh oh! Make sure to fill in all the fields.
                                </div>
                            <?php } ?>


                            <input type="text" name="first_name" class="signup_input" id="first_name_input" placeholder="First Name" value="<?= $_GET['first_name']; ?>" required>

                            <input type="text" name="last_name" class="signup_input" id="last_name_input" placeholder="Last Name" value="<?= $_GET['last_name']; ?>" required>

                            <input type="text" name="email" class="signup_input" placeholder="Email" value="<?= $_GET['email']; ?>" required>

                            <input type="password" name="password" class="signup_input" placeholder="Password" required>

                            <input type="radio" name="gender" value="Female" required> <font color="#FFF">Female</font> &nbsp;
                            <input type="radio" name="gender" value="Male" required> <font color="#FFF">Male </font>

                            <input type="submit" name="submit" class="btn btn-default" value="Sign Up" style="margin-left: 15px;">

</form>

But my login form works.

                    <form action="<?php echo plugins_url( 'login_submit.php', __FILE__ ); ?>" method="post" autocomplete="off">

                      <div class="list-block">
                        <ul>
                                <span class="ti-user"></span>
                                <div class="item-input">
                                    <input type="text" name="email"  placeholder="E-Mail">
                                </div>
                            <div class="item-content margin-top-15">
                                <span class="ti-lock"></span>
                                <div class="item-input">
                                    <input type="password" name="password"  placeholder="Password">
                                </div>
                        </ul>
                      </div>
                      <div class="log-in-btn margin-top-15 margin-bottom-30" >
                        <input type="submit" name="submit" class="btn btn-default">
                      </div>
                      </form>

I am confused as to what the difference is that would cause this.

Answer 1

Use plugins_url()

<form action="<?php echo plugins_url( 'form_submit.php', __FILE__ ); ?>" method="post" >

Codex Reference https://codex.wordpress.org/Function_Reference/plugins_url .

Edit: Please check in wordpress settings. I think you do not have registration enabled.

Hope it helps.