So regarding ISO 20022 it is just a format for what is sent and read so each party have a common format to use (this is only partially true as institutions like making their own variant of it thats valid ISO 20022, think yaml vs json). Sending it is a completely different story, different financial institutions use different technologies for authentication and transport of these messages (SFTP, SWIFT, exotic custom stuff, etc..). My experience has not been in using ISO 20022 to send payments so maybe the payments space all use SWIFT or something.