Step 1- insure that is not loaded. Use the ramrod or a dowel to check the inside of the barrel- if it does not reach all the way to the nipple, there may be a charge in there.
As said- this is a modern day copy of a muzzle loader. Original did not usually have serial numbers. Remove barrel, give us some good photos of ALL markings on the barrel. Prime clue- if you see the words "black powder" it is a copy.
Mendi (long out of business) was a modern day maker of muzzleloaders- usually in kit form. Along with Jukar and CVA, they were from Ardessa Spain.
Ps- that is not a flintlock- caplock. Uses percussion caps. Usually #11s