Well, first of all hi to everybody, i'm a newbie in this cryptocurrency thing, so a lot of doubts are in my mind these days.
I have this question, looking here for the answer I didn't found yet, basically the subject says it all.
If bitcoin transactions are irreversible, why some platforms (online wallets, exchanges, etc) need X confirmations to "validate" a transaction?
to make sure all fee is paid and so transaction confirm by network. If does not confirm money is useless and go back to sender!!
Transactions without fees can get included into a block too. A block typically have 50kb reserved for that. For a free transaction, you need to have the size below 1kb, all outputs above 0.01BTC and the priority must be high enough. If not enough fees is paid, the merchant can use CPFP and rebroadcast it continuously to reduce the possibility of a double spend.