In the latest episode of The Mandalorian, Din Djarin was finally able to spend some Mon Cala money that he acquired all the way back at the start of season 1. After the Empire fell at the end of Star Wars: Return of the Jedi (which takes place five years before The Mandalorian), currency in the galaxy became a little complicated. Though Imperial credits are still being used, their status as legal tender is somewhat shaky.
Din Djarin raised this issue in The Mandalorian's pilot episode, when Greef Karga attempted to pay him for his recent batch of bounties in Imperial credits. Given that the Empire was responsible for the Great Purge of Mandalore, which led to Din's clan being forced to live underground, there's no love lost between him and the Imperial remnants. Greef offered to instead pay him in Calamari Flan, the currency of the Mon Calamari, warning that he could only pay half the value of the bounties in Mon Cala money. Din accepted the reduced payment, demonstrating how little value he places in Imperial credits.
In The Mandalorian season 2, episode 3, "The Heiress," Mando finally gets to spend his Calamari Flan. After arriving on the estuary moon of Trask, he offered the pieces of Mon Cala currency that Greef Karga had given him in exchange for information about other Mandalorians rumored to be on Trask. On balance, the money was well-spent; though the information led to Din Djarin and Baby Yoda being betrayed by the trawlers they were traveling with, that ambush led to an intervention by the Mandalorians on Trask, led by Bo-Katan Kryze.
Much like real-world currency exchanges, the value of different types of money in the Star Wars universe is entirely dependent on who will accept it, and how stable they believe it is. From Din Djarin's perspective, being paid half in Calamari Flan was worth more than receiving the full bounty in Imperial Credits, and if his view is shared by others across the galaxy then Imperial Credits could indeed become worthless.
The Disney+ show has a unique opportunity to explore the fallout of Luke Skywalker's final victory against Emperor Palpatine and the fall of the Galactic Empire - and it's not all good news. For example, The Mandalorian's season 2 premiere revealed that the mining town of Mos Pelgo on Tatooine had been attacked and enslaved by the Mining Collective after the Empire lost control of it. The fall of the Empire has left a massive power vacuum across the galaxy, and now many different factions are fighting to fill it - including Imperial remnants like Moff Gideon.
It seems that the Mon Calamari and their home planet of Mon Cala have emerged from the war in relatively good shape. The people of Trask are mainly comprised of Mon Calamari and their fellow Mon Cala natives, the Quarren. Though The Mandalorian finds them living hard-working lives on the ocean-covered moon (and they're not very good at fixing spaceships), the value he places in Mon Cala currency indicates that they have found some stability in the wake of the Empire's fall.