Maybe I'm overthinking it. The header says "Banks, S&L's, etc" so that leads me to believe that only income reported on a 1099-INT should be shown here.
It's not really a business. Client invests in mortgage receivables instead of in the stock market
If you loaned your next door neighbor $1,000 and they paid you back $1,050, how would you report the $50 interest income with ProConnect?