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I have asked support and they have confirmed that they do not deem any crypto earnings as legal and valid source of income apart from income made through mining. ...

I earn my money from trading, selling some services and sometimes airdrops and stake tells me I am invalid
This is the shittiest statement i read from a reputed platform today if they are following some regulation then it is stupid too how come it was approved.
I agree, this term should be revised. Mining isn't the only way to acquire cryptocurrency. Anyone can acquire cryptocurrency through freelancing and offering services which can be properly documented through the agreement of both parties.
So now, they only see miners as legal crypto jobs/works others are all illegal, what kind of brain they have.
The assumed money laundering isnt the case, he probably will got a reply about that
This is so dumb.
Whats the reason for suspending the account, what did they say?
Just the sae question i was abiut to ask, what i can deduce from the op's statement is the fact that he may have been involved in some money laundering activities that have led to the stake asking him for such legal documents as proof of funds.
It is very possible, stake is probably suspecting OP to have some shady transactions and used stake as platform to wash that transaction.