Hi everyone

I’ve recently just bought a z3 1.9 98’ with the m44 engine. got it home and drove it spot on. however the other day i drove it to work and when i finished the car wouldn’t start up, no crank nothing. i rang the aa and they said the starter motor is good but there’s no feed getting to it, he suggested it would be the immobiliser switch but im very confused and don’t know how to fix this issue due to me being new to the car community.