Additional features, settings, or issues not covered by specific Microsoft Teams categories
I couldn't find any expense app in the App Center. As a workaround, You can consider using 3rd party expense web app out there that meets your company requirements then you can bring it to Team.
You can bring it to the channel on the MS Team by creating a new tab on the channel. Please ask your Team owner to select "+" on the channel > select website > select URL of 3rd party expense web app.