License For Envato

https://YOUR_SITE_URL

<?php
/**
 * licenseCodeVerifyForm()
 */

class licenseCodeVerifyForm {

    const LICENCE_CALL_URL = "YOUR_SITE_URL";
    const PREFIX = "YOUR_PREFIX";

    private $licenceActivate_error;
    private $licenceDeactivate_error;

    public function __construct() {

        $this->licenceActivate_error = $this->licenceActivate();
        $this->licenceDeactivate_error = $this->licenceDeactivate();

        $this->LicenceHTMLForm();
    }

    public function LicenceHTMLForm(){ ?>
        <h2><?php esc_html_e('License Activation Form', 'TEXT_DOMAIN');?></h2>
        <?php
        $token = get_option(self::PREFIX.'_envato_token');
        $isActivated = get_option(self::PREFIX.'_envato_is_activated');

        if ($token && $isActivated) {
            ?>
            <?php
            if ($this->licenceDeactivate_error) {?>
                <p class="licence_error"><?php echo esc_html( $this->licenceDeactivate_error );?></p>
            <?php }?>
            <p><?php esc_html_e('You can click this button to deactivate your license code from this domain if you are going to transfer your website to some other domain or server.', 'TEXT_DOMAIN');?></p>
            <form method="post">
                <input type="hidden" name="envato_deactivate" value="1">
                <?php wp_nonce_field( 'submit_deactivate' ); ?>
                <?php submit_button( esc_html__( 'Deactivate', 'TEXT_DOMAIN' ), 'danger', 'submit_deactivate' ); ?>
            </form>
            <?php
        } else { ?>
            <?php
            if ($this->licenceActivate_error) {?>
                <p class="licence_error"><?php echo esc_html( $this->licenceActivate_error );?></p>
            <?php }?>
            <form method="post">
                <label for="purchase_code"><?php esc_html_e('Purchase code', 'TEXT_DOMAIN'); ?>
                    (<a href="https://help.market.envato.com/hc/en-us/articles/202822600-Where-Is-My-Purchase-Code-"
                       target="_blank"><?php esc_html_e('Where can I get my purchase code?', 'TEXT_DOMAIN');?></a>)
                </label>
                <input type="text" style="width:100%" id="purchase_code" name="purchase_code"
                       placeholder="Example: 1e71cs5f-13d9-41e8-a140-2cff01d96afb">
                <?php wp_nonce_field( 'submit_activate' ); ?>
                <?php submit_button( esc_html__( 'Activate', 'TEXT_DOMAIN' ), 'danger', 'submit_activate' ); ?>
            </form>
            <?php
        }
    }

    private function licenceActivate() {
        if ( ! isset( $_POST['submit_activate'] ) ) {
            return;
        }
        if ( ! isset( $_POST['purchase_code'] ) || empty( $_POST['purchase_code'] ) ) {
            return 'Please Enter Purchase Code.';
        }
        // Unslash and sanitize nonce
        $nonce = isset( $_POST['_wpnonce'] ) ? sanitize_text_field( wp_unslash( $_POST['_wpnonce'] ) ) : '';
        if ( ! wp_verify_nonce( $nonce, 'submit_activate' ) ) {
            wp_die( 'Are you cheating?' );
        }
        if ( ! current_user_can( 'manage_options' ) ) {
            wp_die( 'Are you cheating?' );
        }
        // Unslash and sanitize purchase_code
        $purchase_code = isset( $_POST['purchase_code'] )
            ? sanitize_text_field( wp_unslash( $_POST['purchase_code'] ) )
            : '';

        if ( $purchase_code ) {
            $url    = self::LICENCE_CALL_URL . "/wp-json/licenseenvato/v1/active";
            $domain = $this->domain();
            $itemid = get_option( self::PREFIX . '_envato_itemid' );

            $response = $this->apicall( $url, $purchase_code, $domain, $itemid );
            $data     = json_decode( $response );

            $token  = isset( $data->token )  ? $data->token  : '';
            $itemid = isset( $data->itemid ) ? $data->itemid : '';
            if ( $token ) {
                update_option( self::PREFIX . '_envato_is_activated_' . $itemid, true );
                update_option( self::PREFIX . '_envato_token', $token );
                update_option( self::PREFIX . '_envato_purchase_code', $purchase_code );
                update_option( self::PREFIX . '_envato_itemid', $itemid );
            } else {
                $statusCode    = isset( $data->code )    ? $data->code    : '';
                $statusMessage = isset( $data->message ) ? $data->message : '';
                if ( $statusCode ) {
                    return $statusMessage;
                }
            }
        }
    }

    private function domain() {
        $domain = get_option( 'siteurl' );
        $domain = str_replace( 'http://',  '', $domain );
        $domain = str_replace( 'https://', '', $domain );
        $domain = str_replace( 'www',      '', $domain );
        return urlencode( $domain );
    }

    private function licenceDeactivate() {
        $code = get_option( self::PREFIX . '_envato_token' );
        if ( ! isset( $_POST['submit_deactivate'] ) ) {
            return;
        }
        // Unslash and sanitize nonce
        $nonce = isset( $_POST['_wpnonce'] ) ? sanitize_text_field( wp_unslash( $_POST['_wpnonce'] ) ) : '';
        if ( ! wp_verify_nonce( $nonce, 'submit_deactivate' ) ) {
            wp_die( 'Are you cheating?' );
        }
        if ( ! current_user_can( 'manage_options' ) ) {
            wp_die( 'Are you cheating?' );
        }
        // Unslash and sanitize envato_deactivate
        $envato_deactivate = isset( $_POST['envato_deactivate'] )
            ? sanitize_text_field( wp_unslash( $_POST['envato_deactivate'] ) )
            : '';

        if ( $envato_deactivate ) {
            $url      = self::LICENCE_CALL_URL . "/wp-json/licenseenvato/v1/deactive";
            $response = $this->apicall( $url, $code );
            $date     = json_decode( $response );

            $statusCode    = isset( $date->code )    ? $date->code    : '';
            $statusMessage = isset( $date->message ) ? $date->message : '';

            if ( $statusCode === 'already_deactivated' ) {
                delete_option( self::PREFIX . '_envato_is_activated' );
                delete_option( self::PREFIX . '_envato_token' );
                delete_option( self::PREFIX . '_envato_purchase_code' );
                delete_option( self::PREFIX . '_envato_itemid' );
            } elseif ( $statusCode ) {
                return $statusMessage;
            } else {
                delete_option( self::PREFIX . '_envato_is_activated' );
                delete_option( self::PREFIX . '_envato_token' );
                delete_option( self::PREFIX . '_envato_purchase_code' );
                delete_option( self::PREFIX . '_envato_itemid' );
            }
        }
    }

    private function apicall( $url, $purchase_code, $domain = null, $itemid = null ) {
        if ( $domain ) {
            $body = array(
                'code'   => $purchase_code,
                'domain' => $domain,
                'itemid' => $itemid,
            );
        } else {
            $body = array(
                'token' => $purchase_code,
            );
        }

        $headers  = array( 'Content-Type' => 'application/json' );
        $response = wp_remote_post( $url, array(
            'method'  => 'POST',
            'headers' => $headers,
            'body'    => json_encode( $body ),
        ) );

        return $response['body'];
    }
}
?>

<?php new licenseCodeVerifyForm(); ?>

$response = wp_remote_post( 'https://YOUR_SITE_URL/wp-json/licenseenvato/v1/active', [
    'headers' => [ 'Content-Type' => 'application/json' ],
    'body'    => json_encode( [
        'code'   => $purchase_code,
        'domain' => urlencode( $domain ),
        'itemid' => $item_id,
    ] ),
] );
$data = json_decode( wp_remote_retrieve_body( $response ) );
// $data->token — store this token; you will need it for deactivation

require_once __DIR__ . '/update-checker.php';
new My_Prefix_Update_Checker(
    __FILE__,                          // plugin main file
    '1.0.0',                           // current version
    '12345678',                        // your Envato item ID
    'https://YOUR_LICENSE_SERVER_URL'  // this WordPress site
);