Update
Not an elegant solution, but it works…
I started out trying to program an esp 32 to trigger the camera
and managed to write the code to send the correct bluetooth command (volume up or down) to trigger the shutter. However I didn’t manage to program the bluetooth pairing, so i gave up. This week I had an idea, what about using a trigger that pairs with the camera and then triggering the trigger with the esp 8266. Photo shows the purchased trigger (£2.99, the yellow thing with two buttons click on the photo to see it). I took the circuit board out of the trigger and connected it to the power from a Wemos D1 Mini. I then soldered wires either side of one of the buttons and connected them to a relay which is connected to the Wemos D1 Mini. I then programmed the Wemos to close the relay for 100ms every 20 seconds. This allows me to take a shot every 20 seconds and because its not in timelapse mode, the camera works out the exposure for each shot. Problem solved, now I can take timelapses without having to press the shutter for each shot.