Hello, i have a strange phenomenon…
If i upload my picture (10001.jpg), then it shows in the backend as jpg.10001 and this leads to not being found, if i want to assign it to a product… 
My REST Resource is like that:
api/v1/_action/media/d36e1b73af984b8eb6ce62c82ac9dda8/upload?extension=jpg&fileName=10001
Seems to be correct… where is my mistake ?
EDIT:
I tried with renaming the image to “test10001.jpg” and now everything is ok…
So it seems this function has a problem with a filename, if only numbers are in the filename…
Any idea for a workaround ?
best regards
Holger