You get EUR/USD 1 store credit back basically these 3 games are free. Region restrictions apply in my case keys can only be activated in EU region (I surmise the same for NA based customers)
I can confirm you can buy even if you're in their XP program already
https://www.greenmangaming.com/games/xp-pack-summer-2021/
Instant XP Access
€1 Credit Back
Last Inua Steam Key
Town Of Light Steam Key
Close To The Sun Steam Key
Exclusive vouchers
20% off RRP Voucher for Tribes of Midgard RJ9D4N-YQ2KLD-XN0XI5
23% off RRP Voucher Life is Strange True Colors N44M0K-AUKOSF-3ASB9S
23% off RRP Voucher for Deathloop C6LMDB-5HO87M-QBBMJG
23% off RRP Voucher for Marvel's Guardians of the Galaxy 6DDOG3-RG9ZGY-PK2UP1
For finding games for less than EUR/USD 1 to spend your store credit: