Magento 2 Api Getting Error '%fieldName is a required field'?

Update the function comments correctly for both Interface file and class that implement it.

interface TestInterface
{
    /**
     * Returns greeting message to user
     *
     * @param int $name
     * @return mixed
     */
    public function test($id);
}

You are Sending POST Request so you also have to send data in POST request in json format like :{ "id": {}}

And have to set Content-Type:application/json in http header.