How to set a separate instance for each user


My app is not optimized for symultaneous users, so for the time being, I want to try running it with only 1 connection per instance with 3 instances (basic plan).

What are the settings that should be set ? I tried max workers=1, max connections=1,
start_count = 3 and instance load factor 1.

And I did add 2 more instances manually in the application screen

But the result is that only one instance is currently able to run. Others get HTTP 503

It boils down to - no matter what settings I try new instances are simply not being added when more users connect ...