Upvote:2
Some accounts, such as military ones, could only be settled in specie.
In exchange for a note of hand, a banking house or network offers a more fluid form of cash. The note of hand is discounted: for every £100 of face value, only £85 are supplied. The note becomes due in a certain number of years. (Say 3 years). The bankers have to be paid in specie or another acceptable currency at the end of the period.
Sovereign default or dispossession of individual bankers wasn't unheard of by the way. Nor was direct extraction of specie from banks. Another form of extraction was forced ennoblement with the loan being "discharged" by noble title.
So bankers are concentrating and moving specie in exchange for discounted paper.