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How to get a non-changeable bitcoin address. I tried to register on few bitcoin wallets websites but on each website btc address is changed after one payment is received and I didn't find the option to create a non-changeable one. I know that for privacy is much better to have a changeable btc address, but I need to create a non-changable btc address
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With the majority of wallets, you'll be presented with a new address for each payment. As you mentioned, this is important for your financial privacy, so it is a standard practise.
That said, you can re-use an old address, and your wallet should detect the additional transactions received at that address, updating your balance accordingly.
In short: your wallet is a collection of addresses, it is not just 'the address that is currently displayed'. So you can re-use old addresses from the wallet if you so desire.
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Whilst what you say is true for many online wallets, it is not the case predominantly for desktop (or server) installed wallet software.
In Bitcoin Core, you generate a new receive address, set a label if you like, and forever send BTC to that address.
