How to send 0.0000004 BTC?
Tell me please if there are any services that allow sending such small amounts?
If bitcoin price is $109000, that is around $0.0436. That is too small but you can make use of your wallet to send it. Set the fee to 1 sat/vbyte. The mempool is not congested, it will be confirmed.
40 satoshi? I'd use the lightning network for that. But then if you don't already have them in the lightning network, you would need to pay more to convert them to LN.
1 input and 2 outputs on bitcoin noncustodial wallet in a transaction will not take more than $0.16. If he is patient and ready to learn, he can go less than 1 sat/vbyte
using the guide below.
How to make a bitcoin transaction and pay less than 1 sat/vByte