Forget all those variations like \'1' and \"1", you don't need them. The following should work fine:
If not then there is no such row to update.
What is in $item_number?
Code:
$user_links->update ( { Transaction_ID => $txn_id, PayPal_Email => $payer_email, Used => 1 }, { SetID => $item_number } )If not then there is no such row to update.
What is in $item_number?