There are several competing currency systems in the galaxy. Almost all of them are regional; racial governments and factions often preferring to have their own currency, instead of using something more easily interchanged with the rest of the galaxy. However, due to the practical realities caused by intragalactic trade, the concept is falling out of favor. Using actual currency is seen as an archaic and backwards practice.
That does not mean, however the the concept of money has loosened it's grip on people's lives. Instead, the concept of credits have replaced the concept of 'dollars' or 'yuan', or whatever else. While the credit system works very different from traditional financial systems, most people don't understand (or care about) the difference. To them, it's just another way to get paid, or owe debt.
Each race / faction has it's own unique history with currencies that color their current practices.
The Terrans have standardized on the 'New Yuan', a currency created after the formation of the People's Republic. It was the backbone of their hybrid capitalist/communist economy until after Second Contact, when the credits system was established.
Today, credits are the backbone of their economy, despite the legal requirement that all business transactions happen in yuan. Terran corporations just accept the extra step of converting from yuan to credits and back again. The government is content with that because they take a 1% tax on all currency conversions.
The League, being a relatively recent governmental entity had the opportunity to establish a more sensible system when they established. Despite the urging of the NorAellians, they established the 'League Dollar' as their official currency. All government (and government contractors) are paid in dollars, as well as dollars (including paper/coin currency) being the preferred form of currency on most League worlds.
Unlike the Terrans, however, there's no compulsion to use dollars (with the exception of government contracts).
Most Freelancers don't use anything other than credits. It works well enough for their needs, and bartering is always a valid options where credits would prove annoying.
There are, however, some worlds or coalitions that use their own currencies, but they're seen as niche and a bit eccentric for the practice.
While NorAellians had the concept of non-barter based systems, they had naturally tended towards socialist and communist economies. While personal ownership was certainly a concept (and something they valued quite a bit) trading that ownership always seemed the most practical concept to them. Creating some sort of fiat means of exchange just seemed like barter-with-extra-steps.
NorAellians have never had their own currency (or even true financial system). After encountering other races which did, they fond the concept fascinating and did a lot of research on it, but they simply adopted others system in their interactions, never using them for themselves. Rather practically, they believe that 'wealth' is a measure of what you own, not what you could own. (Most also don't value wealth much at all.)
The Lyndri had their own capitalist society before the Pandemic. Prior to the Monarchy, each pride had their own system (most were barter, but some had moved on to currency based exchanges and trade) it was only after the formation of the Monarchy that they standardized on a global capitalist economy. That was going strong right up till the Pandemic.
Since the collapse of most of their society, the Lyndri have simply adopted whatever system the NorAellians recommended. They were used as a pilot program for the current credit system, and have switched over to credit entirely.
The NorAellians established the Galactic Bank and as it's primary department, the Galactic Credit Bureau (GCB). This was done as an attempt to force the Terrans and League to financially depend on each other enough that war was simply impossible. (Even now the NorAellians believe that this strategy will work in the end.)
The GCB was established as a neutral party not beholden to any government or race. It's board is made up of Humans, NorAellians, and even a few Lyndri. It is the largest, most powerful non-affiliated organization in the galaxy. If they wanted to, they could ruin the economies of all the major governments in a single move. To have your access to credit suspended by the GCB is an instant death sentence for that particular person or group.
The NorAellians came up with a credit system they believed would help alleviate some of the flaws with traditional currency based systems, such as wealth accumulation, excessive debt, or an imbalance in purchasing power simply because of one's location/home faction. How successful it is varies, unfortunately.
Every person, entity, group, etc (called a 'client') is given a Credit Rating. That rating comprises of two parts. The first is how risky this credit line is considered, and the other is a unitless number that is how many 'credits units' the client has been allocated. This is their 'line of credit'.
The term 'credit' is a short-hand for the official term, 'Credit Unit'. While most people treat it as a currency, it's really just a unitless number that only has meaning relative to the credit system as a whole. A credit is simply worth whatever someone is willing to pay for it (generally in good or services).
To use your credit, you simply give some of your credit units ('credits') to another client. Your credit line has now been 'used' by that many credits. You can only use up to your credit limit.
The only way to replace used credit is by receiving credits from from another client. You cannot purchase credit, only transfer it. So once your credit is used up you must get another person to give you credits in order to use your credit line again.
The most interesting part of this system, however, is the fact that you also cannot receive more credits than your current credit line. So if you have a credit line of 1,000 credits, and someone tries to give you 1,000,000 credits, you will only receive whatever amount of credits it takes to free up your credit line to the 1,000 credits. They will be forced to keep the rest.
Besides trading credit units, credit lines can also be transferred. In essence, any client with a credit line can choose to underwrite another client. This means that while a client may have a credit line of 1,000 from the GCB, another organization with large credit line might (according to whatever terms they wish) lend that client an additional credit line of 2,000. This means their maximum credit is now 3,000, though only 1,000 of that is "guaranteed". Should the organization lending the credit not have enough credit units to cover their lent credit line usage, the transitions will be denied.
The primary use case for borrowing credit lines is to allow organizations to authorize large purchases beyond an individuals credit line, or for businesses to allow employees access to additional credit to facilitate their job.
Because the risk of a line of credit is correlated with one's family and their history, it was decided that credit lines can be inherited. When a client closes their account (typically death or disbanding of the group) they can choose to have their credit line converted into a 'hereditary' credit line and list another client (or clients) to have inherit this credit line. At the time of account closing, an evaluation is done on those clients and determination is made on how much of the credit line they will be authorized to access.
(In the event that there is already a hereditary credit line, the new line would simply roll up into the previous one.)
These inherited lines of credit, however are not the same as the individuals line of credit. That is always tied directly to their personal credit rating. Inherited lines of credit are like borrowed lined of credit, but you're borrowing from the GCB itself. Poor behavior or a drop in one's personal credit rating can have the GCB revoke access to these hereditary credit lines. On the same token, they can increase access to these credit lines if a client's credit rating increases.
Over time, these hereditary credit lines are rated like clients; if they perform well and are well managed, they will see their credit lines increase. If they are poorly managed, they will have their credit lines reduced. This is to help promote responsible management of these long-lived credit lines.
The GCB has a long list of criteria for how they establish credit ratings. This criteria is secret, and is fluid. However, there are a few well accepted contributors to credit rating: history of credit usage, the individual's occupation, and the age of the line of credit. If one wishes to increase their credit line, they can schedule a personal consultation with the GCB. A 'Credit Adjuster' will be assigned the case and will work with the client to establish actionable requirements to reach their stated credit line goal. Depending on the desired increase, these could be as simple as improving their credit use habits for a month, or as draconian as selling their failing business or ending their criminal empire.
The GCB, being neutral, doesn't care about the legality of someone's employment when establishing a credit rating. To them, a pirate's job can be just as risky as a humanitarian giving aid in the middle of a war zone. They require accurate information about a client's job, but they will never give that information over to law enforcement. To them it's not their place to pass judgement on the legality or morality of a client, simply on the risk.
That being said, however, individuals who have attacked the GCB, or been responsible for egregious crimes against sentient life have had their lines of credit suspended. It is a very serious action that the GCB does not take lightly.