I cannot resolve this error please help

Unsupported operand types: string / int in C:\xampp\htdocs\luxurytrees\wp-content\plugins\easy-watermark\src\views\dashboard\pages\watermarks.php:26 Stack trace: #0 C:\xampp\htdocs\luxurytrees\wp-content\plugins\easy-watermark\src\classes\Core\View.php(109): include() #1 C:\xampp\htdocs\luxurytrees\wp-content\plugins\easy-watermark\src\classes\Core\View.php(129): EasyWatermark\Core\View->render() #2 C:\xampp\htdocs\luxurytrees\wp-content\plugins\easy-watermark\src\views\dashboard\wrap.php(23): EasyWatermark\Core\View->__toString() #3 C:\xampp\htdocs\luxurytrees\wp-content\plugins\easy-watermark\src\classes\Core\View.php(109): include(‘C:\\xampp\\htdocs…’) #4 C:\xampp\htdocs\luxurytrees\wp-content\plugins\easy-watermark\src\classes\Core\View.php(129): EasyWatermark\Core\View->render() #5 C:\xampp\htdocs\luxurytrees\wp-content\plugins\easy-watermark\src\classes\Dashboard\Dashboard.php(99): EasyWatermark\Core\View->__toString() #6 C:\xampp\htdocs\luxurytrees\wp-includes\class-wp-hook.php(303): EasyWatermark\Dashboard\Dashboard->page_content(”) #7 C:\xampp\htdocs\luxurytrees\wp-includes\class-wp-hook.php(327): WP_Hook->apply_filters(”, Array) #8 C:\xampp\htdocs\luxurytrees\wp-includes\plugin.php(470): WP_Hook->do_action(Array) #9 C:\xampp\htdocs\luxurytrees\wp-admin\admin.php(259): do_action(‘tools_page_easy…’) #10 C:\xampp\htdocs\luxurytrees\wp-admin\tools.php(40): require_once(‘C:\\xampp\\htdocs…’) #11 {main} thrown in bla bla

I get this error, but when I use it on other websites, all is fine. I have tried disabling all plugins one by one, but it didnt change anything.