Creating a virtual store to buy some products

Hello folks.

I am creating a virtual store between Power Apps - SPO list - Excel DB table and Power automate.

My App works on the next way:

- First the user access to the app and check his/her credit ($)

- After that he/she moves to another window to add the articles on the cart.

- With a button I send the purchase to a SPO list with the Name of the client, price per item, total price, quantity

- I am consuming the Name of the client, the ID of the client, and the Credit from an Excel DB table.

- I created a Power Automate flow to check when a new item was created on the SPO list - Get the items from the SPO list - Get the table using the Excel DB - List the rows and - updating a row on the table.

I cannot complete the task on the flow to send the total price spend on the purchase and reduce the total of the credit that the user has on the Column named Money in the Excel DB, instead to do that the value is being replaced for the new one.

I would like your suggestion how to achieve this, how to reduce the total of credits for every purchase of the users from the Power automate flow.