They are very difficult to identify...
The way I have identified mine in the past is to use the Numista descriptions... then find the exact KM number of that coin and compare it to the one I am identifying...
In my experience... It is VERY tedious to identify Tangkas...
Yours looks like an earlier variant of the Tangka (not the ones from the 1900s) but I could be mistaken...
Here are the Numista links to the 1800s Tangkas and the 1900s Tangkas (Just In Case):
1840-1899:
https://en.numista.com/catalogue/pieces15217.html
1899-1930:
https://en.numista.com/catalogue/pieces18922.html
If its 1840-1899 then it is absolutely Type C:
"Type C: The Obverse shows 3 dots in the outer angles and a single wavy water line below the lotus flower
with a changed order of luck symbols. The design of the lotus flower has changed and shows 3 small leaves to the left and right with a wavy water line in the outer angles." I don't know the exact year.
But if it is 1899-1930 then I do not know because none of them seem to have a different order of luck symbols :)
Hope this is helpful,
ShadowyEnigma