help with routes (only works for numbers)

I have a URL

https://localhost/style/S50506/

shows 404 not found, instead of opening a page.

but I also have

https://localhost/style/50506/

and this opens perfectly fine. only different is "S" in front of the number (so i am assuming that postslug is only matching if it is numeric).

Following route is already added:

style/[slug:postslug]

I don't know what is wrong. can you help?