Help with network / visibility failure?

This is kind of open-ended, because at the heart of it is: my subsonic server ran well for a couple of years, but is now invisible outside my home network. Whatever changed, it was months ago - because this is a 'just for fun' project for me that waits until summertime when I have some time. With networking, I know precisely enough to be dangerous, so thanks in advance for the kindness of strangers.
On the LAN, everything behaves fine. My music files are AIFFs and MP3s spread across two NASs, and I see their directories and they play fine. On a device outside the house, no go.
Internally, under Settings / Network, the 'Automatically configure . . . ' box is checked, and I have this message in gray:
Below that, the 'Access your server . . . ' box is checked, and I have this:
So I'm wondering where else to start looking.
How does the URL know to point at my home network? Is there a beacon I should be updating with my IP address?
I think I paid $24 for two years of the Subsonic URL - if my lease were up there, how would I know?
Thanks in advance. In case it helps in any way, my vanity URL is richmilnix.subsonic.org/ .
On the LAN, everything behaves fine. My music files are AIFFs and MP3s spread across two NASs, and I see their directories and they play fine. On a device outside the house, no go.
Internally, under Settings / Network, the 'Automatically configure . . . ' box is checked, and I have this message in gray:
Status: Successfully forwarding port 4040 and port 4443.
Below that, the 'Access your server . . . ' box is checked, and I have this:
Status: Successfully registered web address.
So I'm wondering where else to start looking.
How does the URL know to point at my home network? Is there a beacon I should be updating with my IP address?
I think I paid $24 for two years of the Subsonic URL - if my lease were up there, how would I know?
Thanks in advance. In case it helps in any way, my vanity URL is richmilnix.subsonic.org/ .