homework and exercises - Two different solutions for the expression of potential energy of a uniformly charged solid sphere

I am a bit confused because I did some rigorous derivation of potential energy of a uniformly charged solid sphere and got two different solutions.(Sorry for the long exercise)

Now have a look at my 1st approach:-

I got the general result in my 1st approach which can easily be found in any textbook.

Now have a look at my 2nd approach:-

I got two different results and the second expression is numerically less than the first expression.I want to ask about this ambiguity of two different results for the same problem. I assumed the reference point to be infinity in both derivations and the solid spheres are non conducting.