Ask about process, never about power
How were purchases of this size approved here previously? Who signs at this value? What does the path look like once we have agreed commercially? Is there budget allocated, or does this require a new allocation? These questions are welcomed, because the answers help the buyer manage their own internal work.
Asking who has the authority sounds like preparation for going around your contact. It produces defensiveness and, frequently, a misleadingly confident answer.
Confirm by behaviour
An economic buyer engages with commercial terms rather than features, challenges the business case and the alternatives, can move the timeline when it suits them, and refers to the money as theirs. Someone who talks about submitting the proposal upward, or who cannot say when a decision could be made, is not the economic buyer however senior their title.
Reach them through your contact
Request an introduction with a reason that serves your contact: confirming the outcome and the approval path so that no time is lost later. Going around the person who brought you in damages the relationship the deal depends on, and rarely produces a better meeting than asking properly would have.