I must be missing something about Binance double investment function, please help me understand

EDIT: sorry everyone for wasting your time, the mistery's been solved - I just overlooked a very clear clause of the function!

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Hi guys, I have recently discovered double investment on Binance and I have been studying it just for curiosity's sake.

There's one thing I don't understand about the "sell high" option.

If you are sure that you will earn a margin from your future guaranteed sale, why don't everybody do that repetedly?

Suppose you have $10k to invest. I know, that's not a small amount, but it is affordable for some people.

You buy ETH at $2k at market price, so you buy 5 ETH. You subscribe to double investment to sell those 5ETH at $2.2k in 3 days. After those days you sell your ETH for a total of $11k + the small interest in ETH guaranteed by the product. This means that you have earned $1k over three days (not sure about these values.

Of course there's the chance that market price rises to more than $2.2k, so you miss some profit there.

But that's a chance, whereas the double investment contract guarantees you that you'll have your $1k profit in 3 days. I'd rather have a guaranteed profit of $1k than have a chance of a profit of $1.3k.

And moreover, unless i'm missing some terms of the contract nobody stops you from doing this again and again, thus earning a big profit ever few days.

What am I doing wrong? Because I clearly am!

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Thanks :)