Missing trailer load Ford F150… what to do? Too low maximum ZGG?

Hey, I wanted to get a pedestal with ABE for max 3.5 ton of trailer load on eBay, as I would like to take the class BE driver’s license soon. Again for safety reasons in the vehicle papers and what do I have to see there? Under O.1 and O.2 absolutely nothing is registered. Today immediately with the local TÜV examiner on the phone and he said that I should buy the AHK anyway. And then with this + the values of Ford USA come to him and then one can enter a pedestal afterwards It was very friendly, but somehow I’m uncomfortable to buy this thing if I don’t have any certainty that I can really pull the truck. In addition, he said that he can’t enter more than the maximum permissible weight of the F150. There’s about ~2,83To in my bill. My emptiness already weighs ~2,6To. How can that be? That’s not true, that I can only charge just under 230kg in the debris? I’d like to have the 3,5To trailer load. With my combination si nd according to Ford USA 7700lb possible, have even the tow package as factory option. What is your recommendation? Can you do anything at the maximum permissible total weight? Greeting, Johannes