audio/amr files validation in Laravel

I'm trying to upload an audio/amr file, but always get validation errors.

I tried:

'file1' => 'required|mimes:amr',

and

'file1' => 'required|mimetypes:audio/amr',

but without success.

I also tried to add audio/amr into /etc/niginx/mime.types:

audio/amr    amr;

The only way to pass the validation is to specify application/octet-stream mime type.

I think I missed something. Please, help!