[WordPress] An example for how to properly add multiple sections to a WordPress options page. These gists demonstrate what *not* to do, and what *to* do.

acme-init-section-one.php

<?php

add_action( 'admin_init', 'acme_admin_init_one' );
function acme_admin_init_one() {

	add_settings_section(
		'acme-settings-section-one',      // String for use in the 'id' attribute of tags
		'Acme Settings Part One',         // Title of the section
		'display_acme_settings_message',  // Function that fills the section with the desired content
		'acme-options-page'              // The menu page on which to display this section. Should match $menu_slug.
	);

	add_settings_field(
		'acme-input-field',              // String for the 'id' attribute tags
		'Acme Input Field',              // Title of the field
		'render_acme_input_field',       // Function that fills the field with the desired inputs as part of the larger form.
		'acme-options-page',             // The menu page on which to display this field
		'acme-settings-section-one'      // The section of the settings page in which to show the box
	);

	register_setting(
		'acme-settings',     // A settings group name.
		'acme-input-field'  // The name of an option to save.
	);

}

function display_acme_settings_message() {
	echo "This displays the settings message.";
}

function render_acme_input_field() {

	$input = get_option( 'acme-input-field' );
	echo '<input type="text" id="acme-input-field" name="acme-input-field" value="' . $input . '" />';

}

acme-init-section-two.php

<?php

add_action( 'admin_init', 'acme_admin_init_two' );
function acme_admin_init_two() {

	add_settings_section(
		'acme-settings-section-two',
		'Acme Settings Part Two',
		'display_another_acme_settings_message',
		'acme-options-page'
	);

	add_settings_field(
		'acme-input-field-one',
		'Acme Input Field Two',
		'render_acme_input_field_two',
		'acme-options-page',
		'acme-settings-section-two'
	);

	register_setting(
		'acme-settings-two',
		'acme-input-field-two'
	);

}

function display_another_acme_settings_message() {
	echo "This displays the second settings message.";
}

function render_acme_input_field_two() {

	$input = get_option( 'acme-input-field-two' );
	echo '<input type="text" id="acme-input-field-two" name="acme-input-field-two" value="' . $input . '" />';

}

add-acme-options-page.php

<?php

add_action( 'admin_menu', 'add_acme_options_page' );
function add_acme_options_page() {

	add_options_page(
		'Acme Options',             // The text to be displayed in the title tag
		'Acme Options',             // The text to be used for the menu
		'manage_options',           // The capability required to display this menu
		'acme-options-page',        // The unique slug name to refer to this menu
		'display_acme_options_page' // The function tooutput the page content
	);

}

display-acme-options-final.php

<?php

add_action( 'admin_menu', 'add_acme_options_page' );
function add_acme_options_page() {

	add_options_page(
		'Acme Options',
		'Acme Options',
		'manage_options',
		'acme-options-page',
		'display_acme_options_page'
	);

}

function display_acme_options_page() {

	echo '<h2>Acme Options</h2>';

	echo '<form method="post" action="options.php">';

	do_settings_sections( 'acme-options-page' );
	settings_fields( 'acme-settings' );

	submit_button();

	echo '</form>';

}

add_action( 'admin_init', 'acme_admin_init_one' );
function acme_admin_init_one() {

	add_settings_section(
		'acme-settings-section-one',      
		'Acme Settings Part One',         
		'display_acme_settings_message',  
		'acme-options-page'               
	);

	add_settings_field(
		'acme-input-field',        
		'Acme Input Field',        
		'render_acme_input_field',  
		'acme-options-page',        
		'acme-settings-section-one' 
	);

	register_setting(
		'acme-settings',    
		'acme-input-field'    
	);

}

function display_acme_settings_message() {
	echo "This displays the settings message.";
}

function render_acme_input_field() {

	$input = get_option( 'acme-input-field' );
	echo '<input type="text" id="acme-input-field" name="acme-input-field" value="' . $input . '" />';

}

add_action( 'admin_init', 'acme_admin_init_two' );
function acme_admin_init_two() {

	add_settings_section(
		'acme-settings-section-two',
		'Acme Settings Part Two',
		'display_another_acme_settings_message',
		'acme-options-page'
	);

	add_settings_field(
		'acme-input-field-two',
		'Acme Input Field Two',
		'render_acme_input_field_two',
		'acme-options-page',
		'acme-settings-section-two'
	);

	register_setting(
		'acme-settings',
		'acme-input-field-two'
	);

}

function display_another_acme_settings_message() {
	echo "This displays the second settings message.";
}

function render_acme_input_field_two() {

	$input = get_option( 'acme-input-field-two' );
	echo '<input type="text" id="acme-input-field-two" name="acme-input-field-two" value="' . $input . '" />';

}

display-acme-options-incorrect.php

<?php

function display_acme_options_page() {

	echo '<h2>Acme Options</h2>';

	echo '<form method="post" action="options.php">';

	do_settings_sections( 'acme-options-page' );
	settings_fields( 'acme-settings' );
	settings_fields( 'acme-settings-two' );

	submit_button();

	echo '</form>';

}

display-acme-options.php

<?php

function display_acme_options_page() {

	echo '<h2>Acme Options</h2>';

	echo '<form method="post" action="options.php">';

  	do_settings_sections( 'acme-options-page' );
  	settings_fields( 'acme-settings' );

  	submit_button();

	echo '</form>';

}