curve fitting anomaly in Curve Fitting App

I need to curve fit my data to y(x) = 1/(b+a*(1-exp(-x/c)))

I'm getting completely different values when I do this in Python vs. Matlab. I've never had issues using curve fitting in Matlab, and I'm wondering why I'm getting horrendous R^2 values. This model is supposed to theoretically fit my data with an R^2 of 0.99, and I'm unclear why this is happening?

x = [500
1000
1500
2000
3000
4000
5000
6000
8000
10000
100
200
300
400
500
600
700
800
900
1000
1200
1517]

%
y = [1.82542E-08
1.60033E-08
1.42392E-08
1.35091E-08
1.24128E-08
1.14393E-08
1.06488E-08
9.97894E-09
9.00539E-09
8.58287E-09
2.09938E-08
2.03239E-08
1.95938E-08
1.8924E-08
1.82542E-08
1.77674E-08
1.73429E-08
1.67335E-08
1.64297E-08
1.58806E-08
1.53335E-08
1.44223E-08]