Cannot purchase trucks - requirements not fulfilled

I cannot purchase any vehicle, because the requirements are not met. However, I think my airport meets the requirements for a pushback vehicle, namely, a vehicle depot and a road checkpoint:

Version is 28.1.10, savegame was started in 28.1.8, I think.

Pebkac or bug?

Is it sandbox or regular gameplay? Also do you have Procurement agency?

is your depot properly connected?

Has your road to the edge of map completed building?

@Antarctica please provide us more information and even screenshots in order to help you: