In the AAMVA 16-step tractor-semitrailer coupling procedure, which of these actions is performed last?

AAMVA CDL Manual, Section 6.4.1, Steps 11-16, p. 6-8 to 6-9

Doing these steps out of order can be dangerous. Removing the wheel chocks before the coupling is verified and the trailer brakes are reliably holding could let an improperly coupled trailer roll. Following the sequence ensures every safety check happens before the rig is driven away.