When I try to select a file for a POST multipart/form-data request, I get an error notification in the bottom-right corner of my screen: Couldn't upload file. Make sure that Postman can read files inside the working directory.
I resolved this error by downloading the postman desktop app instead of using the web version. Then, navigate to Settings, under General and Toggled on the option “Allow reading files outside working directory”
I believe this will help you too...