I activated sniper to bid on an item in my absence over the weekend. It didn't happen! There were no other bids and the item (120438579590) was not sold. Sniper shows the bid is still active, what did I do wrong?

Welcome to our forums.

You've done everything right.

If you check the snipe status, you will see the following:
"The seller ended this listing early".

If you open the auction's page, it has:
"The seller ended this listing early because the item is no longer available for sale.".

That means that the seller ended his/her auction earlier for some reason (probably decided not to sell).
The best thing you can do is to search another similar item or contact the seller and ask if this item is still for sale.

Thanks, missed that