Fatal error with PHP 8.0 and above

If I use PHP 8.0 or above I get this error when trying to login in /wp-login.php page:

Fatal error: Uncaught Exception: subcript_period parameter must be integer in SwpmUtils::calculate_subscription_period_days method in /home/spodf.pt/public_html/wp-content/plugins/simple-membership/classes/class.swpm-utils.php:59 Stack trace: #0 /home/spodf.pt/public_html/wp-content/plugins/simple-membership/classes/class.swpm-utils.php(82): SwpmUtils::calculate_subscription_period_days() #1 /home/spodf.pt/public_html/wp-content/plugins/simple-membership/classes/class.swpm-utils.php(90): SwpmUtils::get_expiration_timestamp() #2 /home/spodf.pt/public_html/wp-content/plugins/simple-membership/classes/class.swpm-auth.php(186): SwpmUtils::is_subscription_expired() #3 /home/spodf.pt/public_html/wp-content/plugins/simple-membership/classes/class.swpm-auth.php(122): SwpmAuth->check_constraints() #4 /home/spodf.pt/public_html/wp-content/plugins/simple-membership/classes/class.swpm-auth.php(246): SwpmAuth->authenticate() #5 /home/spodf.pt/public_html/wp-content/plugins/simple-membership/classes/class.simple-wp-membership.php(422): SwpmAuth->login() #6 /home/spodf.pt/public_html/wp-includes/class-wp-hook.php(324): SimpleWpMembership->wp_authenticate_handler() #7 /home/spodf.pt/public_html/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters() #8 /home/spodf.pt/public_html/wp-includes/plugin.php(565): WP_Hook->do_action() #9 /home/spodf.pt/public_html/wp-includes/user.php(78): do_action_ref_array() #10 /home/spodf.pt/public_html/wp-login.php(1309): wp_signon() #11 {main} thrown in?/home/spodf.pt/public_html/wp-content/plugins/simple-membership/classes/class.swpm-utils.php?on line?59

Is this a known problem? Using latest version of plugin.