We lived in apt. when we brought Letty home. I kennel trained and took her out frequently. I also picked up her water bowl after a certain time at night. A month in we bought the potty patch to have as an option for our convenience. I would watch for signals like going to door or circling and I would hold her on patch using key word potty. If she went I would give her a treat. If she didn't go, I would keep an eagle eye on her or put her back in kennel since I knew she wouldn't go in there. Then let her out and straight to patch again with treat in hand to give if she used it.
We have no confusion and now have house on acreage. We still have patch in house and like it as when we go to visit family, we take it with and she knows to look for it. She is always a welcomed guest and I have no problem getting someone to dig watch when we cruise
I don't recommend using leash, I'd stick to the harness when outside. It is much better for their little necks and avoids damage to throat. I agree with what DBlain said about going out but not letting them wander around when harnessed to go potty. Take them where you want them to go and eventually they will almost always go to same place. After they go you can let them off lead to play and run. Then they look forward to going potty and getting it out if the way so they get treat and free time
Side note... Since we kennel trained and took outside our pup would not use pee pads when we tried to introduce as an option. We had to use potty patch as it felt like the grass she'd become used to.