An Architect to notify by the Business that order conversion dramatically dropped a few hours...

The appropriate tool to verify that the problem is indeed caused by the inventory check at the beginning of checkout is the Pipeline Profiler in Business Manager. This tool allows an architect to analyze the performance of specific code execution paths, including those involving third-party API calls. It helps identify bottlenecks and inefficiencies in the pipeline execution, particularly useful in situations where custom code like inventory checks may impact site functionality. The use of the Pipeline Profiler would enable the architect to pinpoint if the custom inventory check is causing the checkout process to fail or redirect users inappropriately.