Certain cryptocurrencies require a memo, tag, or note when sending from one wallet to another wallet. The main reason for this is that it allows the wallet provider to know which account the cryptocurrency belongs to. This is especially applicable for exchange wallets, as the exchanges use the tag, memo, or note to link a wallet to the account of the associated customer. Some networks use a tag others do not.
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​Note: If the tag/memo is not entered correctly, this could lead to a loss of cryptocurrencies. Always check if you are sending through the right network, this is indicated at the wallet address you want to send to.