Incorrect responses by the AI Agent on totals

Summary:

We created an AI Agent to provide the invoice information to user when asked.

This agent will also list all the invoices entered for the given supplier.

Based on the listed invoices, when we ask what is the total spend it responds with some random amount (same random amount is displayed constantly). The amount doesn't match with the total invoice amount for the given supplier. It is almost doubled/three times the actual invoice totals.

We also included Calculator tool in the agent, still the same random amounts.

How to find the calculation that the agent is performing to get the total spend?