I reported it as well.  This same app was on Google Play last year and scammed a bunch of people, I think Google only got around to removing it after Coindesk did an article about it being a scam.

Some future advice for anyone installing sensitive content from the Play Store: Check for fake reviews. This one has a 4.6 rating and lots of 5 star reviews but once you read them you can tell somethings wrong- Ratings are all from same 2 day period, all have similar writing style, avatars all look similar (this one has a bunch of reviews from attractive white guys in suits), English sounding names but very bad English in the reviews, duplicate reviews from different people. The only 3 reviews that appear to be from real people are all saying that the app is scam.

Sorry you got robbed OP, I hope it wasn't for too much and you are able to bounce back.

1. Betking is in the wrong because in his OP he simply asks people to take his survey and never says that he'll only pay for positive feedback.
2. He is probably doing this survey so he can look through the results and find positive quotes/statistics that he can use to promote his site. I don't think lying and saying "Everything is perfect bla bla" is the right thing for you to do if you think a site is shady because that would mean you are helping to promote something that you think is a scam- which would make you just as bad as him.

I've never been on the site and don't know if it's legit or not, but the fact that the owner has not kept his word in paying everyone for their surveys is enough for me to not trust him or his site.

No risk when using PayPal as long as you check the "for goods or services" box as PayPal transaction type. It charges a couple extra dollars but that is for insurance, if the person does not send the item you can open a PayPal dispute and PayPal will refund your money. Scammers will tell you to check "friends or family" box because those transactions are not insured by PayPal.

Just buy from someone with good feedback, use PayPal and you will be ok. I have ordered 100s of things from eBay and only had 1 problem where the item did not come but PayPal refunded me my money when that happened.

Your best bet would probably be to search "jailbroken iphone" or "unlocked iPhone" on eBay. And don't worry, you write very good English- I am American and I can understand you perfectly 

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He also offered- without being asked- to send the funds "as a gift"; Paypal doesn't allow chargebacks when choosing the friends/family option.

OP You made a bunch of mistakes and now you are SOL. Use this as a learning opportunity to protect yourself better in the future.