Please check the blogs from Gunther: https://blogs.sap.com/2023/04/02/sap-build-apps-and-bapis-rfc-meets-web/ and https://blogs.sap.com/2023/04/04/rfc-meets-the-web-building-the-proxy/ 

I found the answer from Mari in the AppGyver community: https://forums.appgyver.com/t/how-do-you-format-currency/6225 You can do that with the FORMAT_LOCALIZED_DECIMAL 11 formula function.