Alliance currency is generally accepted in all places, but some smaller facilities and remote locations choose to control their local economy through the distribution of 'trade vouchers', which are allowed by law if they meet certain criteria. For example, a mining facility which sees little or no outside traffic might control the rise and fall of the Alliance Credit and the local value of money and inflation through the distribution of their own mandated currency. Some corporations, slavers and the like will issue locally printed and backed credits as a control mechanism, and as 'trade vouchers' are allowed under the limitations of any micro-economy that fits within the regulations of trade and commerce as dictated by the UAP, some people take advantage of their employees and citizens by restricting the flow of outside currency.
There are also groups, companies, etc. who may choose to issue local currency for the soul purpose of quiet defiance, such as Independents that haven't 'come in from the cold' since the end of the war. These Browncoat factions may choose their own currency as a protest, using the laws of trade and commerce to their own advantage. A sort of independent day to day in a highly allied Verse.
Trade vouchers are also used when there are enough world currencies being passed about in a single local economy that it creates confusion, such as a border world which might deal in goods and services backed by bills printed on dozens of different worlds. While all of these currencies might seem 'unified' in value, the use of a virtual credit versus 'cashy money' can be somewhat diversified from one local economy to another, paving the way for many an aspiring corporation, governor or subversive, underground potentate in a shiny hat to make money and maintain control. A hand in every pocket , as it were.
For this reason, travelers are advised to check for the 'Trade Voucher' mark when making change. This mark can be the difference between valuable folding money on one world and very fancy toilet paper on another. Of course, some people choose to keep vouchers, as many travelers do, because money is just fun to collect.
One of the more interesting bills to bear the voucher mark comes out of a roving, restless freeport called Solace. Made up of dozens of new and old ships, the ever growing Solace is a space station on the move and a city nation in it's own right. Inhabited primarily by veterans and loyalists of the Independent movement, the citizens of Solace choose to maintain a commerce free of the Alliance name, but well within the regulations of the loopholes of the same. They will gladly, and fairly exchange your credits for theirs, if only to keep Alliance currency out of sight and out of mind. After all, at the end of a long day no Independent worth his brown coat should have to pay for food, clothing and shelter with the Alliance's blood money.
I've created these four up to a page, double sided and with 8 different numerical series to keep the numbers unique, and to add a little variety to your cash money collections.
http://pics.fireflyprops.net/PACE-Solace1Credit-A.pdf
http://pics.fireflyprops.net/PACE-Solace1Credit-B.pdf
http://pics.fireflyprops.net/PACE-Solace1Credit-C.pdf
http://pics.fireflyprops.net/PACE-Solace1Credit-D.pdf