Not complaining here, just trying to help sort out the glitch. I just tried different browsers and disabled both adblock and the enhanced steam extensions. The issue is still there.  I don't know if that will help you diagnose, but I thought I'd try to help out by eliminating things to look at.

my account is having the same issue. cant redeem my Es2 rewards nor the Es1 free pack. hope it gets fixed soon. even though my account details show im already linked to steam the rewards page keeps asking to link a steam account.

Fixed for me. Thanks again Cat-O and everyone for being so diligent!

I have been experiencing the 

• ERROR_USER_STEAM_EXIST

problem since i join here back on 3/2018, I feel  I have miss out on loads of thngs. love the game/developer but this game2gether problems puts me off. I try ever time there is a free weekend but always the same. So it cant be a tempory problem if i have been having it coming upto a year!

If admin see this please look into my account. or contract me by email please.

Same here... 

• ERROR_USER_STEAM_EXIST

I cannot redeem my endless space collection. It said that I must contact an administrator. But theres no link to valid support...

same here

Working nice to me.

For those of you who get the ERROR_USER_STEAM_EXIST message, this message comes up if the Steam Account has already been linked. Have you had a G2G account before, or have you attempted linking before?

If neither is the case, I will talk to the web team to see what is causing the issue, though I may need to ask you for further information via direct message.