Offer provider companies pay us for getting them offer completions. For example, an iPhone app developer pays us for getting them downloads on their app! We then use this money to purchase ROBUX to payout our users.
Offer completions are decided by the offer provider, and each provider is different. Some reasons for offers not crediting could be the information inputted was flagged as spam, your ad-blocker caused problems with tracking, or simply the offer is bugged. In some cases, it can take a few hours for an offer to credit!
Unfortunately, we are unable to credit completions from our end, only the offer provider can decide if an offer is completed or not. If you are 100% sure that you completed the offer correctly and have waited over 24 hours, you can try contacting the company providing the offer for assistance. If you are having difficulties completing desktop offers, try switching to a mobile device; there are plently of easy app download offers to complete!