Keep external URL

Hi! I have a wordpress multisite installed in a subdirectory. “quomarmi.com/inventory” I use your Redirection plugin to pass an external URL to one specific site in the principal wordpress installation “quomarmi.com”
ex: stock.alfaquistone.com goes to —> quomarmi.com/inventory/alfaquistone

My question is: I want to keep that “external” URL (stock.alfaquistone.com) when somebody comes in: and keep it like: stock.alfaquistone.com/product/dark-emperador-polished-slabs-2cm-a44/

how can I do it properly?

Thank you!

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