If it's too large it says...
View attachment 1337609
Not supported can be because of a number of other reasons. Bad XML, wrong SVG version, wrong number of bits in the file encoding (16-bit instead of 8-bit for example).
Not quite.
The maximum file size is 15,360 Bytes. 15,360 bytes dived by 1024 bytes in a kB = 15kB.. so the number you really want to be looking at is the size in bytes...
This file is exactly on the limit, 15,360 bytes, which equals 15kB exactly - 1 byte more and it won't upload. It shows in the status bar summary as 14.9kB...
View attachment 1337610
The point being, go by the size in bytes, it must be 15360 or less.
This is interesting, it sounds like that program is re-writing matrix transforms in gradients, which would be a big plus for people struggling with how badly some programs write gradients. Out of curiosity, does it work with skewed radial gradients?