Hi, the dimmers can be hard to connect and may take multiple tries. Unfortunately, there is no way to see a successful connection in the app as the Philips Hue bridge does not show 3rd party smart controls to apps.
The only indication you have is the LED pattern the dimmer shows when using touchlink. That needs to be exactly the same as in the video. After that you can connect the dimmer to the lights (keep in mind it won’t be visible in the app). What exactly goes wrong when connecting the dimmer? Did you wait 10 seconds after resetting the dimmer? Is the LED pattern of your dimmer the same as in the video?