I measure 2.8V between GPIO4 and ground when set to high, and 0 when set to low.
I don’t think the output can drive a LED by itself, but I’m not that into electronics so can’t say for sure.
If you still can’t set GPIO and measure high/low on it without any load connected to it, you should provide more information such as what firmware you’re using and what SDK version you’re using.
I was told that OpenAT 3.02/FW 6.51 is very buggy and should not be used.
I know first-hand that it contains quite a few bugs, but when I used it I’m decently certain that I had GPIO4 working.
3.69V definitely sounds odd though.
You should ask your supplier for SDK 3.03 if possible. 3.10 or 3.12 works too, but with those you may need modifications in your program.
Or check the hardware for any short-circuits that could affect the outputs, as well as make certain that you’re measuring the right pins… (pin 53 for GPIO4) and if possible, check on another module if the problem stays the same.