How to send 0.0000004 BTC?
Tell me please if there are any services that allow sending such small amounts?
You can send 0.0000004 BTC from your wallet, I think you will not have any problem. But I want to know what wallet are you using? If you are using an exchange, then maybe you will not be able to send 0.0000004 BTC because there is a minimum withdrawal that will not allow you, but if you are using your own wallet like Trust wallet, Safepal wallet, Electram wallet, etc., then I think you can send this amount of 0.0000004 BTC.