I recently purchased something online with my debit card and when I check my online account it shows that I have spent nothing. I bought the item about 2 days ago so maybe it just needs to update from the bank?
Such transactions do not show up in "real time." Often several days elapse between when you make the transaction and when it posts.
The company could be slow at processing debit card orders and your bank is slow at posting them. It will probably show up tomorrow. Especially since you used your debit card. Banks don't process on Sunday.