You have to process your document once with pdflatex, then once with biber and then twice again with pdflatex.
With this example (modified from the linked question to use beamer):
\documentclass{beamer}
\usepackage[style=verbose]{biblatex}
\usepackage{filecontents}% to embed the file `myreferences.bib` in your `.tex` file
\begin{filecontents*}{myreferences.bib}
@online{foo12,
year = {2012},
title = {footnote-reference-using-european-system},
url = {http://tex.stackexchange.com/questions/69716/footnote-reference-using-european-system},
}
\end{filecontents*}
% File is created and written to disk by the above package
\addbibresource{myreferences.bib}
\begin{document}
\begin{frame}
Some text.\footnote{Some text in a footnote.} Some more text.\footcite{foo12}
\end{frame}
\begin{frame}
\printbibliography
\end{frame}
\end{document}
The output is:

Check your versions for biblatex and update if necessary. In my system, TeX Live2015, at the moment of this answer:
biblatex.sty 2015/04/19 v3.0 programmable bibliographies (PK/JW/AB)
biblatex2.sty 2015/04/19 v3.0 programmable bibliographies (biber) (PK/JW/AB)
Biber 2.1
\footfullcitefrom this answer https://tex.stackexchange.com/q/416247/117274 and then report back if possible. Or have you found out how to solve the mystery yourself, then kindly answer your own question. – thymaro Feb 20 '18 at 17:47