Potty training – he doesn’t show signs

Hi all, I need help.

I'm a first time puppy owner, he is just 16 weeks old and I got him last weekend. At the moment because he didn't finish his vaccinations, the vet advised not to bring him out. Thus, I am unable to do outside potty training.

Without a crate now, I am using a playpen with a pee tray inside. At first he doesn't pee on the pee tray successfully, so I halfed his playpen.

Currently, the area is small. With enough area to play and a pee tray to potty. However, it's a hit and miss.

I have 2 issues I need help, 1. How do I increase his chance of pottying in the pee tray 2. He always go potty just when I look away. I can't catch his rhythm/behaviour.

Any tips for the above? Thank you very much 😭