I have been given " Watch only Address" by one of my friends.
To make the funds credited into my account or to use the BTC, what is way to get the private key?
Do we need to pay anything to blockchain.info for releasing? Is the from my friend who is hiding the private key?
I have been given " Watch only Address" by one of my friend
This is a scam often used by online con-men posing as your friend.
A watch only address lets you watch a bitcoin wallet owned by someone else. They can move their bitcoins away at any time. You cannot spend their bitcoins.
Do we need to pay anything for the blockchain.info for releasing
No. If your "friend" claims to have earlier set up an online wallet for you and that the online service now need paying to release the private-key - your "friend" is lying to you in order to cheat you out of your money.
The Blockchain.info website has a link "Get a Free wallet". If your "friend" used that, they got a private-key for free. Note that this wallet belongs to them, not to you. That applies even if it appears to contain money that you gave to your "friend" or which they claimed to earned on your behalf by mining or trading.
blockchain.info's terms of services paragraph 10.2 says
When you create a Wallet, the Services generate and store a cryptographic private and public key pair that you may use to send and receive any supported Virtual Currency
So there is no cost to obtaining the private key when you create a free wallet.
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