Hi,
Thank you for uploading the files. The warning seems to not be relevant (I would need to fix this).
To avoid it, you can just run with a different eps when calling TF1::IntegralError (e.g. 1.E-6)
Change line 63 of your code to be:
double Z_sig_err = dcb->IntegralError(z_sig_min,z_sig_max,nullptr, nullptr, 1.E-6);
Lorenzo