There are a few reasons why the rear washer isn't working. The rear washers share the same reservoir with the front washers. If the front is working then it's safe to say you have washer fluid

Trace the 6mm black rubber hose under the back seat and make sure it hasn't separated at a joiner. Look for puddles on the floor. Fill the washer reservoir right up so you can see the level in the filler neck then operate the rear washer for 10 secs or so. If you can hear the pump operating but the fluid level does not drop there is likely an obstruction in the hose.
On my 2Q2023 delivered vehicle the rear window washer hose was tightly wrapped inside the wiring harness to the rear door and was squashed to the point where it stopped working. The fix advised by IA to my agent was to separate the hose from the harness. That's a fair bit of work to split the harness open then wrap it again so if an obstruction seems to be the case for you ask your agent for assistance.