Missing FeynMF labels in TeXworks 0.6.6

Question

I wrote the following code to depict a sum of two diagrams. I usually used only overleaf but given the dimension of the document I am writing I needed to download and use TeXworks. However, the aforementioned diagram, which worked on overleaf, now does not show any label. I red the entire guide for that package (feynmf) but still I cannot understand what I am doing wrong.

\documentclass{book}
\usepackage{feynmf}
\begin{document}
\begin{center}
\begin{fmffile}{gzzexample4}
    \parbox{80pt}{\begin{fmfgraph}(50,50)
    \fmfleft{i1,i2}
    \fmfright{o1}
    \fmf{dashes}{i1,v1}
    \fmf{dashes}{v1,i2}
    \fmf{photon}{v1,o1}
    \fmflabel{$\tau$}{i1}
    \fmflabel{$\tau$}{i2}
    \fmflabel{$\tau$}{o1}
    \fmflabel{$\tau_1$}{v1}
    \fmfv{decor.shape=square,d.size=3thick}{i1,i2,o1}
    \fmfv{decor.shape=circle,decor.filled=empty,d.size=3thick}{v1}
    \end{fmfgraph}}
    $+$\parbox{100pt}{\begin{fmfgraph}(50,50)
    \fmfleft{i1,i2}
    \fmfright{o1}
    \fmf{dashes}{i1,v1}
    \fmf{dashes}{v1,i2}
    \fmf{photon}{v1,o1}
    \fmflabel{$\tau_1$}{i1}
    \fmflabel{$\tau_1$}{i2}
    \fmflabel{$\tau_1$}{o1}
    \fmflabel{$\tau$}{v1}
    \fmfv{decor.shape=square,d.size=3thick}{i1,i2,o1}
    \fmfv{decor.shape=circle,decor.filled=empty,d.size=3thick}{v1}
    \end{fmfgraph}}
    \end{fmffile}
\end{center}
\end{document}