Swift Pro - Can't teach manually


I’ve just unpacked and assembled the uArm Swift Pro with the gripper. Now I’m trying to teach the robot manually (no software/offline) following this guide (Offline Learning Mode): http://download.ufactory.cc/docs/en/uArm-Swift-Pro-Quick-Start-Guide-1.0.pdf

I click the “Start recording” button, move the arm around a bit, switch the on/off the suction cup gripper, stop recording and then play.

But nothing happens when I click the play button. The gripper just moves slightly to the left. What to do?