Budget wrote:
I'm trying to calculate the principal payment for $19,855,000 @ 6.25%
interest rate over 15.5 years with 1 principal payment per year.

"15 1/2 years"? When is the fractional-period payment made: (1) at
the end of the half-year before the 15 annual periods; or (2) at the
end of the half-year after 15 annual periods?

I'm trying to calculate the interest payment for $19,855,000 @ 6.25%
interest rate over 15.5 years with 2 interest payments per year

What exactly do you mean by "interest payments"? Do you mean simply
that interest compounds semiannually? Or do you mean that __you__
actually make a payment mid-year that is equal to interest accrued
during the half-year? In other words, are you making unequal payments
semiannually?(!)

What is the compounding frequency: (1) semi-annually; or (2) something
more frequent (specify)?

I suggest that you clarify the terms of the loan. Specifically, you
omitted the regular (or irregular) payment amount(s); and you omitted
the interest compounding frequency.