I haven't done any work with MongoDB, but I assume from the following:

# delete a document
$coll->delete_one( { name => "John Doe" } );
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... that you can delete a single document given its ID by using:

$coll->delete_one( $doc );
# or maybe
$coll->delete_one( { _id => $doc->{_id} } );
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Thank you very much for getting back.

Now I see what you typed it is hard to imagine why I didn't see my mistake in not having $coll as s startpoint to change the collection.

Happy I can proceed.