Please Help. BMW 5 SERIES F10 Not starting

Hi, I’m new to this forum and BMW in general.

I purchased the car in December 2021, it’s a 520d 62 plate automatic and the current mileage is 75k). As far as I can tell, it’s had full service history and was due for a service now.

As I’m driving home, I approached a set of traffic lights and as I came to a stop, travelling at around 5mph, the car cut out and would not fire back up, it would crank for as long as I’m holding the ignition Button but would not fire.

I’ve been given an error code ‘P0087’ by and obd2 device.

Trouble Code: P0087 Fuel Rail/System Pressure – Too Low

I’ve had a mobile mechanic come out and have a look, he bled the injectors and the engines getting plenty of fuel, he then checked the battery which was on low health so we replaced the battery which didn’t change the outcome of starting the car up.

He then tried all sorts of tricks using the obd2 and still nothing, his final diagnosis is that it must be the timing chain. But I’ve yet to have confirmation on this because it’s pending a compression test, whatever that means.

I also asked the mechanic about fuses, relays and sensors to which he said ‘if it was a fuse, it would come up on my machine’.

I’ve had non-mechanics check the car prior to this and they have insisted that if it was the timing chain, it wouldn’t be cranking.

it’s worth noting that until this moment, the car hasn’t skipped a beat, no knocks or bangs or rattles, even when it broke down.

any ideas Or solutions or advice would be greatly appreciated as I simply do not have the funds to fix a timing chain.

Thank you.