Error 501 when connecting BubbleUPnP with Volumio

When I try to stream music from BubbleUPnP to Volumio, I am getting the “Error 501” message. Volumio is correctly displayed as a renderer in BubbleUPnP on my phone, but I can’t stream anything from it to Volumio.
I am using wired connection for the Pi and the WiFi from the same router for my phone.
Does anyone have any ideas?