Hi there! how did you find out about that rebate offer?? There is some offers that are available only for some players,My guess is that you will usually play mtts tournaments, if you were a spin and go regular player the promo will be oriented to Sping and go tickets and so on..
If you got the promo via e-mail,it should say the code for your offer in there (check at your spam mail folder just in case). If it says about it once you open the Pokerstars client,you should find the code by opening Cashier> then clicking on the "my rebate status" button,and there you will have all the info.normally they do link a web page with all details about the offer (such the amount of stars points required if needed or cash out NOT available condition during the offer) .
I would say the only condition in your case will be to make the deposit and probably you instantly get a 50€ tournament money ticket..don't think you must use it all at once in a single tournament, but it could be also a chance that the ticket is for a specific MTT,probably the ME of microseries.