@BagusOkta
gold and silver are materials that have real value.
The problem would rather be with too many copper coins, or worse if he used gold coins and silver coins to buy the copper coins and keep them to himself, it would block the local economy
In addition it is not a few coins that will have an effect on the complete system, especially in the middle ages
There is a lot of physical money sleeping in these periods, at worst it will have the same economic effect as preparation for a war (moment when the lord spends a lot of money on equipment, resources, mercenaries, .. .)
This kind of big appearance of money had a very positive effect on the local economy.
It is when there are not enough resources to buy that it could pose a problem
in this case there will be too much money and it will lose its value
Let's say he has a lot of money to spend, having a house built will create the value of the money he will give to the workers
Buy an unused one and the money will be spent by the former owners, you will make repairs, modifications, ..
Our system works on the creation of value through human work, so the work and the appearance of money must be fair.
A kingdom that does not create enough money will see the value of his money increase, but it will only be locally
This kind of fluctuation is normal, but it was not really seen in our middle ages, because most people didn't even use money and the information was not traveling very fast