Answer
This is typically because the underlying IFS Component that provides that specific BizAPI simply isn't installed on the second system — for example, a distribution-related inbound-transactions BizAPI is bundled with a specific component, and if that component isn't installed, its BizAPIs won't appear in the Soap Gateway's list at all, regardless of routing configuration. Check the Installed Components window to confirm whether the relevant component is actually installed on the system in question; if it isn't, the customer needs to request and install that component from IFS before the corresponding BizAPI/handler becomes available.