Trying to set up Site Path Routing - end up getting 404 errors

Hello everyone here.  Please help with advice and ideas
I have a tough task of crossbreeding 2 websites based on 2 different technology stacks.
I have website 1 a.k.a https://www.abc.com which is running on WordPress on LAMP server and this is the public website.
I have website 2 a.k.a https://commerce.abc.com and this is a custom developed ecommerce system running on IIS, the whole application is written in VB.NET.
My intention is to make website 2 to open within the context path of website 1 so it looks to the visitors like website 2 is running inside the website 1; something like https://www.abc.com/commerce
With this plan I set up Site Path Routing in the following manner:
 
Site Path Routing
 
My problem is that when I access website 1 everything is good, but once I add manually the path https://www.abc.com/commerce I get 404 error suggesting that website 1 does not have such path.  For the sake of experiment I tried creating a folder ‘commerce’ inside website 1 and disabling the SPR rule but then the error naturally changes to 403 Forbidden suggesting that I am not allowed to browse the folders.

My question – what am I doing wrong about site path routing setup?  Is what I am trying to do achievable?