Greetings sweet_tikka welcome to the Forum
Sounds like you need to use an old "Camping" tactic, given that
your little one may just be slow on "getting in the mood".
You say you don't have a closed yard, ok...
I've used 1/4" Nylon Rope. Tied it to a Screw Eye near the back
door, and stretched it overhead to a tree limb, about 25' away
from the door. It's runs about 7' off of the ground, so you can
walk around under it.
I put a Roller Clip on the Rope, and have a spare Leash on it,
where I can just take my little one outside, snap the Leash
onto it's harness, and just leave him there for as long as needed !
Now, he has a "Doggy Run", where he can sniff and dwell on thinking
about pottying, while I'm drinking Coffee inside, and watching him.
You probably can get this done for under $10.
This help ?