How I can know how many bytes my transaction have? It's just send btc from one wallet to another
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How do you know it's need 2-3satoshis/byte
maybe this page
https://coinb.in/#fees is more informative and easy to use for you
but you need to understand a basic knowledge on different types of bitcoin addresses
it gives you recommended fee with
minimum feerate, you could use a bit higher rate if you want