The curl code is not included in the released software (there are other software packages we use as well that we do not release as they are released by others). Curl is however installed by the conan package manager before cmake is run (if interested curl and the other software we use are listed in the conanfile.py).
mkdir build
cd build
conan install .. --build missing
qmake ../PBE.pro
make
if on a windows machine, use nmake instead of make. let me know if it does not work for you.