Vili ain't wrong lol. You could give them away as gifts or, what I do, top off my cash purchases with them. So every time I am at the grocery store (often once evert day or two), I will be at self checkout and pay X cash minus what I have on a card, then just press the button for "another payment method" and take my Google Pay with the credit card on it.
I usually only pull out 2$ at a time though, so mine are rarely more than 25 cents. (I know what I will be buying, and it is a $2.60 can of beer. With the exchange rate, $1.96 USD is $2.65 CAD, the exact amount I need, So I am almost never left with more than pennies.
Another super cool use for them, if it works, could be to do a bunch of those "Offers" on Torox/Prime/Etc, that ask you to sign up to some casino and deposit at least $1. The coin payout is worth well over the $1 value. I've never tried that though.
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Yep — try bonus code: SuperSuperSecretBonusCode 
They also drop bonus codes on X sometimes: https://x.com/gain_gg
If it says invalid/used/expired, then it’s probably already been gobbled up by the code gremlins 
More codes are usually dropped randomly, so keep an eye on GAIN.GG’s X here: https://x.com/gain_gg 
For now, try: SuperSuperSecretBonusCode 
If it says invalid/used/expired, the code goblins probably got there first 
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