Welcome!

As far as I understand, you’re currently doing calculations on the fly, and want to store them in the database. For example, if a payment is in GBP, you want to show it as USD.

When the payment is created, do the currency conversion and save the converted USD amount to a usdTotal field on the payment data type (note this method would not be scaleable if you want to support viewing in multiple currencies - in that case you’d have another Currency Conversion data type which has an Amount and a Currency, and store the converted amounts as a list on the payment). I would set this up using a backend trigger (Only when Payment now’s total is not Payment before change’s total → get currency conversion from API → save to Payment now).

You could also do this, but it may be slow and more expensive in terms of WU. You’d create a backend workflow that takes relevant parameters, do what you want, then Return data from API. Call that backend workflow from the API Connector or App Connector (so set up an API call to your own app).