Restrict Image Sizes and Dimensions when Uploading via the WP Mobile App

Try this code in function.php I hope this help.

add_action( 'rest_api_init', 'set_image_dimension_limit' );
function set_image_dimension_limit() {
    add_filter( 'wp_handle_upload_prefilter', function( $file ) {
         $mimes = array( 'image/jpeg', 'image/png', 'image/gif' );

        if( !in_array( $file['type'], $mimes ) )
        return $file;

        $img = getimagesize( $file['tmp_name'] );
        $maximum = array( 'width' => 500, 'height' => 700 );

        if ( $img[0] > $maximum['width'] )
        $file['error'] = 
            'Image too large. Maximum width is ' 
            . $maximum['width'] 
            . 'px. Uploaded image width is ' 
            . $img[0] . 'px';

        elseif ( $img[1] > $maximum['height'] )
        $file['error'] = 
            'Image too large. Maximum height is ' 
            . $maximum['height'] 
            . 'px. Uploaded image height is ' 
            . $img[1] . 'px';

        return $file;
    } ); 
}