In order to make a delicious marmalade of a good consistency, I had to remember mathematics. And the math here is simple. Knowing that agar-agar when diluted with a liquid from 1 to 20 (1:20) gives a solid jelly, you can easily calculate the proportions of the ingredients.
It turns out that for 5 g of agar (and a tablespoon without a top), 100 g of liquid is needed. At the same time, I got the best taste and structure of marmalade at a ratio of 60 g of jam + 40 g of water.
So: for every 5 g (tablespoon) of agar, we take 40 g of water and 60 g of jam. Of course, this amount is very small, you will get only 3-4 jellies, but you can easily increase the number of ingredients at least 10 times.