I don't always recall this problem - but it's been around for at least a year now for me (could be longer).

The issue is spread across iPad, iPhone 6s, iPhone SE all running the latest OS.

The same headphones all work great when connected to an Android device (lowest volume is actually low).

Just like the others mentioned - the volume only controls the iPhone volume. I have three pairs of bluetooth headphones from various brands (Jabra, iFrogz, and another cheap pair) that all are uncomfortably loud at the lowest setting. I have seen some other threads about it, but I'm stunned there isn't even more noise about this. Do you understand why your response doesn't help anyone?

After looking for quite some time, not a single Apple customer service associate has supplied an actual fix for this ridiculous feature. Obviously I do not know what occurred in Apple to cause this but this problem is actually quite a massive flaw, and all of the proof points to Apple relying on circuitous conversation control to convince everyone who asks the problem becomes redirected and somehow convinced that the problem is actually the headphones or some equally implausible explanation. I don't care about headphones/BT peculiarities, Everyone asking this question ( thousands of people if not a factor of 10 more) wants to know how they can change the volume in settings since a large number of heasdsets do not have volume control and the stock minimum volume is way too loud, crazy loud.

That is why no one in any sort of even slightly meaningful position will give a straight answer on this topic. There is no way to reduce the volume below the minimum in iOS, which is a HUGE flaw. This topic s brought up across the internet/across the world. This response adds no value to the discussion.

Make bluetooth headphones louder