TTS-ultimate in a docker container

I really don't know if HTTP Static is the root cause but thats the only difference in between your and my settings, and it plays well for me

// When httpAdminRoot is used to move the UI to a different root path, the
// following property can be used to identify a directory of static content
// that should be served at http://localhost:1880/.
httpStatic: '/data',
// Context Storage
// The following property can be used to enable context storage. The configuration
// provided here will enable file-based context that flushes to disk every 30 seconds.
// Refer to the documentation for further options: https://nodered.org/docs/api/context/
//
   contextStorage: {
	default    : { module: "localfilesystem"},
	memoryOnly : { module: "memory" }
},

if that does not help ... I cant think of anything else ... just to be clear ... after HTTP Static update .. you still have to find the correct path and I would recommend testing with that /data path first

this works for me: http://192.168.1.219:1880/123.mp3