How to upload file using nestjs-graphql-fastify server and how to test such feature?

I struggle to upload .csv file to nestjs-graphql-fastify server. Tried following code:

  @Mutation(() => Boolean)
  async createUsers(
    @Args({ name: 'file', type: () => GraphQLUpload })
    { createReadStream, filename }: FileUpload,
  ): Promise<boolean> {
    try {
      // backend logic . . .
    } catch {
      return false;
    }
    return true;
  }

but all I get when testing with postman is this response:

{
    "statusCode": 415,
    "code": "FST_ERR_CTP_INVALID_MEDIA_TYPE",
    "error": "Unsupported Media Type",
    "message": "Unsupported Media Type: multipart/form-data; boundary=--------------------------511769018912715357993837"
}

Developing with code-first approach.