Hello,

no purchase is needed. All  you need is a Coinbase account , level 2 verified user.

How is working? 

 Invite your friends.

Earn up to an additional $40 in XLM/Comp/Band when your friends start earning.

Basically, you answer at 1 question  from each  coin and you received  10$ and I'll receive 10$.  I won't know who were you so  is fully anonymus  !!

XLM  10$ - https://coinbase.com/earn/xlm/invite/ys4p9r8m

Comp 10$ - https://coinbase.com/earn/comp/invite/60sf2cpk

Band  10$ - https://coinbase.com/earn/band/invite/1ycs9fdt

you can after  witdraw  the coins and do whatever  you want with  them.

In this case I consider it  a win win situation !!