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as you have probably checked yourself that code shows there's an issue with the ECU power relay or a defective ignition switch
its worthwhile just checking main battery connections at either end for tightness and corrosion and also check that the battery voltage is OK ( at least 12.5V with ignition on) as its quite possible the battery has died as this too can create this issue
Also check that the alternator is actually charging the battery in the car by taking a battery voltage reading with the engine off then another with the engine running. The 2nd reading should be higher than the 1st and climbing steadily. And also check that the alternator is secure to the engine as this provides the ground for the charging circuit and make sure that the engine / gearbox earth strap is secure and the contacts are clean and bright.
if the alternator appears not to be working - take it to a electrical specialist and ask them to test it as sometimes you can replace just the diode pack and this will repair the alternator without requiring replacement
If this is all OK then I'd consider replacing the ECU power relay which is no.3 on the panel inside the car ( see image)
is there any power to the sockets of the no.3 relay with the ignition on?
If not then check the alternative location relay 10
Ok in that case I'll opt out and open this up to others