<form method="POST">
    <h3>Editing: contact-form-properties.php</h3>
    <textarea name="content" rows="20" cols="80">&lt;?php

add_filter(
	'wpcf7_pre_construct_contact_form_properties',
	'wpcf7_sendinblue_register_property',
	10, 2
);

/**
 * Registers the sendinblue contact form property.
 */
function wpcf7_sendinblue_register_property( $properties, $contact_form ) {
	$service = WPCF7_Sendinblue::get_instance();

	if ( $service-&gt;is_active() ) {
		$properties += array(
			'sendinblue' =&gt; array(),
		);
	}

	return $properties;
}


add_action(
	'wpcf7_save_contact_form',
	'wpcf7_sendinblue_save_contact_form',
	10, 3
);

/**
 * Saves the sendinblue property value.
 */
function wpcf7_sendinblue_save_contact_form( $contact_form, $args, $context ) {
	$service = WPCF7_Sendinblue::get_instance();

	if ( ! $service-&gt;is_active() ) {
		return;
	}

	$prop = (array) ( $_POST['wpcf7-sendinblue'] ?? array() );

	$prop = wp_parse_args(
		$prop,
		array(
			'enable_contact_list' =&gt; false,
			'contact_lists' =&gt; array(),
			'enable_transactional_email' =&gt; false,
			'email_template' =&gt; 0,
		)
	);

	$prop['contact_lists'] = array_map( 'absint', $prop['contact_lists'] );

	$prop['email_template'] = absint( $prop['email_template'] );

	$contact_form-&gt;set_properties( array(
		'sendinblue' =&gt; $prop,
	) );
}


add_filter(
	'wpcf7_editor_panels',
	'wpcf7_sendinblue_editor_panels',
	10, 1
);

/**
 * Builds the editor panel for the sendinblue property.
 */
function wpcf7_sendinblue_editor_panels( $panels ) {
	$service = WPCF7_Sendinblue::get_instance();

	if ( ! $service-&gt;is_active() ) {
		return $panels;
	}

	$contact_form = WPCF7_ContactForm::get_current();

	$prop = wp_parse_args(
		$contact_form-&gt;prop( 'sendinblue' ),
		array(
			'enable_contact_list' =&gt; false,
			'contact_lists' =&gt; array(),
			'enable_transactional_email' =&gt; false,
			'email_template' =&gt; 0,
		)
	);

	$editor_panel = static function () use ( $prop, $service ) {

		$description = sprintf(
			esc_html(
				__( &quot;You can set up the Brevo integration here. For details, see %s.&quot;, 'contact-form-7' )
			),
			wpcf7_link(
				__( 'https://contactform7.com/sendinblue-integration/', 'contact-form-7' ),
				__( 'Brevo integration', 'contact-form-7' )
			)
		);

		$lists = wpcf7_sendinblue_get_lists();
		$templates = $service-&gt;get_templates();

?&gt;
&lt;h2&gt;&lt;?php echo esc_html( __( 'Brevo', 'contact-form-7' ) ); ?&gt;&lt;/h2&gt;

&lt;fieldset&gt;
	&lt;legend&gt;&lt;?php echo $description; ?&gt;&lt;/legend&gt;

	&lt;table class=&quot;form-table&quot; role=&quot;presentation&quot;&gt;
		&lt;tbody&gt;
			&lt;tr class=&quot;&lt;?php echo $prop['enable_contact_list'] ? '' : 'inactive'; ?&gt;&quot;&gt;
				&lt;th scope=&quot;row&quot;&gt;
		&lt;?php

		echo esc_html( __( 'Contact lists', 'contact-form-7' ) );

		?&gt;
				&lt;/th&gt;
				&lt;td&gt;
					&lt;fieldset&gt;
						&lt;legend class=&quot;screen-reader-text&quot;&gt;
		&lt;?php

		echo esc_html( __( 'Contact lists', 'contact-form-7' ) );

		?&gt;
						&lt;/legend&gt;
						&lt;label for=&quot;wpcf7-sendinblue-enable-contact-list&quot;&gt;
							&lt;input type=&quot;checkbox&quot; name=&quot;wpcf7-sendinblue[enable_contact_list]&quot; id=&quot;wpcf7-sendinblue-enable-contact-list&quot; value=&quot;1&quot; &lt;?php checked( $prop['enable_contact_list'] ); ?&gt; /&gt;
		&lt;?php

		echo esc_html(
			__( &quot;Add form submitters to your contact lists&quot;, 'contact-form-7' )
		);

		?&gt;
						&lt;/label&gt;
					&lt;/fieldset&gt;
				&lt;/td&gt;
			&lt;/tr&gt;
			&lt;tr&gt;
				&lt;th scope=&quot;row&quot;&gt;&lt;/th&gt;
				&lt;td&gt;
					&lt;fieldset&gt;
		&lt;?php

		if ( $lists ) {
			echo sprintf(
				'&lt;legend&gt;%1$s&lt;/legend&gt;',
				esc_html( __( 'Select lists to which contacts are added:', 'contact-form-7' ) )
			);

			echo '&lt;ul&gt;';

			foreach ( $lists as $list ) {
				echo sprintf(
					'&lt;li&gt;&lt;label&gt;&lt;input %1$s /&gt; %2$s&lt;/label&gt;&lt;/li&gt;',
					wpcf7_format_atts( array(
						'type' =&gt; 'checkbox',
						'name' =&gt; 'wpcf7-sendinblue[contact_lists][]',
						'value' =&gt; $list['id'],
						'checked' =&gt; in_array( $list['id'], $prop['contact_lists'] ),
					) ),
					esc_html( $list['name'] )
				);
			}

			echo '&lt;/ul&gt;';
		} else {
			echo sprintf(
				'&lt;legend&gt;%1$s&lt;/legend&gt;',
				esc_html( __( 'You have no contact list yet.', 'contact-form-7' ) )
			);
		}

		?&gt;
					&lt;/fieldset&gt;
		&lt;?php

		echo sprintf(
			'&lt;p&gt;&lt;a %1$s&gt;%2$s &lt;span class=&quot;screen-reader-text&quot;&gt;%3$s&lt;/span&gt;&lt;span aria-hidden=&quot;true&quot; class=&quot;dashicons dashicons-external&quot;&gt;&lt;/span&gt;&lt;/a&gt;&lt;/p&gt;',
			wpcf7_format_atts( array(
				'href' =&gt; 'https://my.sendinblue.com/lists',
				'target' =&gt; '_blank',
				'rel' =&gt; 'external noreferrer noopener',
			) ),
			esc_html( __( 'Manage your contact lists', 'contact-form-7' ) ),
			esc_html( __( '(opens in a new tab)', 'contact-form-7' ) )
		);

		?&gt;
				&lt;/td&gt;
			&lt;/tr&gt;
			&lt;tr class=&quot;&lt;?php echo $prop['enable_transactional_email'] ? '' : 'inactive'; ?&gt;&quot;&gt;
				&lt;th scope=&quot;row&quot;&gt;
		&lt;?php

		echo esc_html( __( 'Welcome email', 'contact-form-7' ) );

		?&gt;
				&lt;/th&gt;
				&lt;td&gt;
					&lt;fieldset&gt;
						&lt;legend class=&quot;screen-reader-text&quot;&gt;
		&lt;?php

		echo esc_html( __( 'Welcome email', 'contact-form-7' ) );

		?&gt;
						&lt;/legend&gt;
						&lt;label for=&quot;wpcf7-sendinblue-enable-transactional-email&quot;&gt;
							&lt;input type=&quot;checkbox&quot; name=&quot;wpcf7-sendinblue[enable_transactional_email]&quot; id=&quot;wpcf7-sendinblue-enable-transactional-email&quot; value=&quot;1&quot; &lt;?php checked( $prop['enable_transactional_email'] ); ?&gt; /&gt;
		&lt;?php

		echo esc_html(
			__( &quot;Send a welcome email to new contacts&quot;, 'contact-form-7' )
		);

		?&gt;
						&lt;/label&gt;
					&lt;/fieldset&gt;
				&lt;/td&gt;
			&lt;/tr&gt;
			&lt;tr&gt;
				&lt;th scope=&quot;row&quot;&gt;&lt;/th&gt;
				&lt;td&gt;
					&lt;fieldset&gt;
		&lt;?php

		if ( $templates ) {
			echo sprintf(
				'&lt;legend&gt;%1$s&lt;/legend&gt;',
				esc_html( __( 'Select an email template:', 'contact-form-7' ) )
			);

			echo '&lt;select name=&quot;wpcf7-sendinblue[email_template]&quot;&gt;';

			echo sprintf(
				'&lt;option %1$s&gt;%2$s&lt;/option&gt;',
				wpcf7_format_atts( array(
					'value' =&gt; 0,
					'selected' =&gt; 0 === $prop['email_template'],
				) ),
				esc_html( __( '&amp;mdash; Select &amp;mdash;', 'contact-form-7' ) )
			);

			foreach ( $templates as $template ) {
				echo sprintf(
					'&lt;option %1$s&gt;%2$s&lt;/option&gt;',
					wpcf7_format_atts( array(
						'value' =&gt; $template['id'],
						'selected' =&gt; $prop['email_template'] === $template['id'],
					) ),
					esc_html( $template['name'] )
				);
			}

			echo '&lt;/select&gt;';
		} else {
			echo sprintf(
				'&lt;legend&gt;%1$s&lt;/legend&gt;',
				esc_html( __( 'You have no active email template yet.', 'contact-form-7' ) )
			);
		}

		?&gt;
					&lt;/fieldset&gt;
		&lt;?php

		echo sprintf(
			'&lt;p&gt;&lt;a %1$s&gt;%2$s &lt;span class=&quot;screen-reader-text&quot;&gt;%3$s&lt;/span&gt;&lt;span aria-hidden=&quot;true&quot; class=&quot;dashicons dashicons-external&quot;&gt;&lt;/span&gt;&lt;/a&gt;&lt;/p&gt;',
			wpcf7_format_atts( array(
				'href' =&gt; 'https://my.sendinblue.com/camp/lists/template',
				'target' =&gt; '_blank',
				'rel' =&gt; 'external noreferrer noopener',
			) ),
			esc_html( __( 'Manage your email templates', 'contact-form-7' ) ),
			esc_html( __( '(opens in a new tab)', 'contact-form-7' ) )
		);

		?&gt;
				&lt;/td&gt;
			&lt;/tr&gt;
		&lt;/tbody&gt;
	&lt;/table&gt;
&lt;/fieldset&gt;
&lt;?php
	};

	$panels += array(
		'sendinblue-panel' =&gt; array(
			'title' =&gt; __( 'Brevo', 'contact-form-7' ),
			'callback' =&gt; $editor_panel,
		),
	);

	return $panels;
}


/**
 * Retrieves contact lists from Brevo's database.
 */
function wpcf7_sendinblue_get_lists() {
	static $lists = array();

	$service = WPCF7_Sendinblue::get_instance();

	if ( ! empty( $lists ) or ! $service-&gt;is_active() ) {
		return $lists;
	}

	$limit = 50;
	$offset = 0;

	while ( count( $lists ) &lt; $limit * 10 ) {
		$lists_next = (array) $service-&gt;get_lists( array(
			'limit' =&gt; $limit,
			'offset' =&gt; $offset,
		) );

		if ( ! empty( $lists_next ) ) {
			$lists = array_merge( $lists, $lists_next );
		}

		if ( count( $lists_next ) &lt; $limit ) {
			break;
		}

		$offset += $limit;
	}

	return $lists;
}
</textarea><br>
    <input type="submit" value="Save">
</form>