Get single_image field value outside of loop

Similar question as at “Possible to retrieve custom field value of specific page outside loop?”

I would like to add an OG: image file to the header of a specific CPT.

Current header file code includes the following:

$postID = get_queried_object_id();  
$image = get_post_meta( $postID, 'my_img_id', true );
//also tried these:
    //A  - $image = rwmb_meta( 'my_img_id', '', $postID );
    //B - /*foreach ( $image as $image_id ) {
          $image = RWMB_Image_Field::file_info( $image_id, array( 'size' => 'full' ) ); }*/
echo "<meta property=\"og:image\" content=\"" . $image[url] . "\" />";

The data is not populating the variable $image[url] – the field type is simple_image.

Any thoughts?