An historical example of needing more money because an economy ran out it and people couldn't get any to do financial transactions:
* https://en.wikipedia.org/wiki/Great_Bullion_Famine
* https://en.wikipedia.org/wiki/Great_Slump_(15th_century)
See also the Great Drepession for another problem with a fixed money supply:
> However, Temin (1989) argues that, once these destabilizing policy measures had been taken, little could be done to avert deflation and depression, given the commitment of central banks to maintenance of the gold standard. Once the deflationary process had begun, central banks engaged in competitive deflation and a scramble for gold, hoping by raising cover ratios to protect their currencies against speculative attack. Attempts by any individual central bank to reflate were met by immediate gold outflows, which forced the central bank to raise its discount rate and deflate once again. According to Temin, even the United States, with its large gold reserves, faced this constraint. Thus Temin disagrees with the suggestion of Friedman and Schwartz (1963) that the Federal Reserve's failure to protect the U.S. money supply was due to misunderstanding of the problem or a lack of leadership; instead, he claims, given the commitment to the gold standard (and, presumably, the absence of effective central bank cooperation), the Fed had little choice but to let the banks fail and the money supply fall.
* https://www.nber.org/system/files/chapters/c11482/c11482.pdf