Amazon UK ppc £100 offer

Hi all. I’ve had the offer from Amazon UK for £100 credit for click. Could someone tell me if, after I’ve used the £100 am I under any obligation to carry on paying? Or can I just carry on using it (and paying) whenever I see fit in the future?

Also, anyone else using this do yo find it effective?

Thanks

Have not seen the offer but I would think that it comes with terms & conditions. Read them very carefully for the answer.