TextMesh Pro How to generate all arabic letter substitutions?

Hi,

I try to get arabic to work. I have a font which contains all arabic letters (I checked with font forge).
I generated a font for TextMesh Pro with this ranges:

But only the Inital version of the characters are generated. Not the middle or final versions.
How can I generate all substitutions?

(I am using TMP 3.0 from the package manager)

 

I found out that there seems to be a problem with the font.
Although there are all substitutions in the font, they seem to not be connected to the right unicodes. Only the General Unicode seems to be present but not the Isolated, End, Middle or Beginning forms (if you don't know what I am talking about, see here).

I use a modified version of BalooBhaijaan-Regular. Does anybody know how I can fix the font?