It’s all metric fasteners, so if you were using an imperial wrench, it may not be a perfect fit. I would soak it in some sort of penetrating oil. If the correct size metric wrench won’t fit, you may also be able to use a slightly larger star bit and tap it in.
Tried this today and stripped set screw on rear sprocket. Thing would not budge!
It’s all metric fasteners, so if you were using an imperial wrench, it may not be a perfect fit. I would soak it in some sort of penetrating oil. If the correct size metric wrench won’t fit, you may also be able to use a slightly larger star bit and tap it in.