Keep in mind that fiat-based currency, like paper, only came about because it was getting annoying and dangerous to carry the actual currency (made of various precious materials) around...which on their own represented how much of a certain item was worth that much (like grain, cattle, or in sometimes even water).
So economic systems evolved from "x number of thing 1 for y number of thing 2" to "a in weight of precious material equal to x number of thing 1 for y number of thing 2" to "b coin(s) that represent a in weight of precious material equal to x number of thing 1 for y number of thing 2" to "c note(s) that equal b coin(s) that represent a in weight of precious material equal to x number of thing 1 for y number of thing 2". Let's ignore that I've simplified this and left out the insanity that is inflation and politics reeking havoc on this otherwise straight-forward process, changing values of any given commodity or service over time, or that I'm not going to address the bullshit that is electronic transfers of currency.
Skipping steps means skipping the critical "Tf is this? Why is it worth that? Why should I care? Do other people agree?" step, and trying to enforce it use...well, force isn't going to work forever. So best to get started with coins and have be a currency that people trust and consider valuable before slowly phasing paper notes via bank-backed invoices (which is how paper notes got their start) and slowly make them paper notes.
The pressure from merchants who deal with the easier to transport currency will force the other nations to adopt them in the long run.
