I am looking at adding a boombox to certain monuments like outpost and bandit camp. I have got the boombox spawning in and powering it. However, I can't figure out how to make it select the audio stream and playing it. Any suggestions?

Which boombox prefab are you spawning and how are you spawning it?

var boombox = GameManager.server?.CreateEntity(BOOMBOX_PREFAB, entity.transform.position) as DeployableBoomBox;
if (boombox == null)
{
  Puts("No deployable boombox found!");
  return;
}

boombox.Spawn();
boombox.SetParent(entity);
boombox.transform.localPosition = new Vector3(0f, 0.85f, 1.75f);
boombox.SendNetworkUpdateImmediate(true);
// Provide power to the boombox
boombox.UpdateFromInput(25, 0);

I see, you're doing this all via code. Likely you want to look into the boom box controller, which is available under boombox.BoxController.

Also, this is a good idea for the Monument Addons plugin. It already allows you to spawn boomboxes at monuments, but maybe a feature can be added so that an admin can configure the boombox to have a preselected station and automatically be turned on.

Thanks. I got it working. Now it's falling off of heli or breaking or something.

boombox.BoxController.ConditionLossRate = 0;
// Turn off the current station
boombox.BoxController.ServerTogglePlay(false);

_CurrentRadioIp.SetValue(boombox.BoxController, "https://.../creedence-clearwater-revival-fortunate-son.mp3");

// Use newly select MP3 stream
boombox.BoxController.BaseEntity.ClientRPC<string>(
null,
"OnRadioIPChanged",
boombox.BoxController.CurrentRadioIp);

// Start playing again!
boombox.BoxController.ServerTogglePlay(true);

I recommend spawning the boombox.static prefab which avoids those problems. It neither breaks nor disappears.