I can't contact the seller

I bought an inventory system but it is not working properly, how can I contact the seller to inform them?

If you visit:

construct.net/en/game-assets/orders

And then press:

"I have a problem with items in an order"

And follow instructions, it will show you their contact details.

Alternatively, if you visit the items page, there is a support URL website link if the seller filled it out.