Secure iOS fax recommendations?

Does anyone know of a secure application to send private financial documents via fax using an iPhone? Security is my main priority here.

For sensitive data, you definitely want to be careful. Here is a helpful ranking of secure options: https://beebom.com/best-fax-apps-for-iphone/. Personally, I swear by Municorn Fax App. I used it to send my tax forms last month. It features excellent encryption, works flawlessly, and provides immediate delivery confirmations, which gives great peace of mind.