calculus – U-substitution for integral of 1/(1+e^x)dx. What am I doing wrong? – Mathematics Stack Exchange

Here is my work, with the right answer. I feel like every step is right, but somehow I am getting the wrong answer. How?$$ \int \frac{1}{1+e^z}dz = \int\frac{1}{e^z(\frac{1}{e^z} + 1)}dz

Source: calculus – U-substitution for integral of 1/(1+e^x)dx. What am I doing wrong? – Mathematics Stack Exchange