Basic PHP code fix (immediate start a must)

I have found a problem with the coding of my website. It is a major problem but thankfully a very minor fix. When a user visits our download page he/she is prompted to complete a quick offer to gain access to the file. When the offer is completed, we receive the postback info & the download should immediately start. Therefore there should be an iframe on the page which is refreshing every 5 seconds to check if the data has gone into the database, as soon as it has then it should redirect the page inside the iframe to the file so that it pops up as a download to the user. This is currently not the case, instead the file is being awarded as a response to the postback, so the user is not actually getting the file but instead the postback system is. All we need is a very basic PHP page that will check the database, and as soon as the details it is looking for appear it will redirect to the file. Please only bid if you are confident you can complete the job to a high standard as security is a MUST, also an immediate start is vital. LOW BIDS WILL WIN.