I've a feeling that a that time, the payment and rewarding of soldiers was done by their Generals, who were toffs with land and money to begin with. So paying off your ranks would be done in lump sums, quite literally a 'division of spoils', and this was pretty much up to the generosity of your general and maybe a bit more from additional charities. A typical reward, that would provide an income, was a pub - look at the number of 'Marquis of Queensbury' pubs as an indication. A 'purse of money' ie a lump sum in cash might be more normal. As everyone is hinting, being able to keep tabs on who went where was difficult, travel was slow and expensive, and sending cash was dodgy - most people did not have bank accounts. In addition, most people died younger and were aware of their mortality, and so a lump of cash would be quite acceptable given that their expectations were not like ours ie living long into our 80s, 90s and beyond.
I think the late Georgian / Victorian reforms of the army brought in regular pensions but it would require at least the existence of post offices for their collection to be safely assured.