A very good loan indeed!

Here is how the problem was set up initially:

$N\left[\text{EffectiveInterest}\left[-\frac{295}{10000},\frac{7}{365}\right]\right] \Rightarrow -0.00995111573462815$

The value that is the solution is the denominator of the APR fraction, i. e., -295.

$\text{Solve}\left[\text{TimeValue}\left[\text{Annuity}\left[\text{payment},\frac{52\ 7}{365},\frac{7}{365}\right],\text{EffectiveInterest}\left[-\frac{295}{10000},\frac{7}{365}\right],0\right]=100000,\text{payment}\right] \Rightarrow \text{payment}\to 1894.38$

Now, the solution:

$\text{Round}\left[10000 \text{rate}\text{/.}\, \text{FindRoot}\left[\text{TimeValue}\left[\text{Annuity}\left[1894.38,\frac{52\ 7}{365},\frac{7}{365}\right],\right.\right.\right.$

$\left.\left.\left.\text{EffectiveInterest}\left[\text{rate},\frac{7}{365}\right],0\right]=100000,\{\text{rate},-0.01\}\right]\right] \Rightarrow -295$

The -0.01 is only an initial guess at the answer. We know that the interest rate has to be negative because the payments do not repay the original loan amount.

This is not as far-fetched as one might think: see Negative interest on excess reserves . It has happened relatively recently in Japan and Europe and is on-the-table for the USA Federal Reserve Bank.