How to add vertical space between subfigure in latex/overleaf

Question

My figures layout is as follows

\begin{figure*}
    \centering
     \begin{subfigure}{0.45\linewidth}
        \centering
        \includegraphics[width=5cm, height=5cm]{m1.png}
        \caption{M1:Correlation graph.}
        \label{fig:m1}
    \end{subfigure}
&
    \begin{subfigure}{0.45\linewidth}
        \centering
        \includegraphics[width=5cm, height=5cm]{m1c.png}
        \caption{M1:Clusters.}
        \label{fig:m1c}
    \end{subfigure}
    \vspace{1cm}
    \begin{subfigure}{0.45\linewidth}
        \centering
        \includegraphics[width=6cm, height=6cm]{m2.png}
        \caption{M2:Correlation graph.}
        \label{fig:m2}
    \end{subfigure}
&
    \begin{subfigure}{0.45\linewidth}
        \centering
        \includegraphics[width=6cm, height=6cm]{m2c.png}
        \caption{M2:Clusters.}
        \label{fig:m2c}
    \end{subfigure}
\vspace{1cm}
    \begin{subfigure}{0.45\linewidth}
        \centering
        \includegraphics[width=5cm, height=6.5cm]{m3.png}
        \caption{M3:Correlation graph.}
        \label{fig:m3}
    \end{subfigure}
&
    \begin{subfigure}{0.45\linewidth}
        \centering
        \includegraphics[width=6cm, height=6.5cm]{m3c.png}
        \caption{M3:Clusters.}
        \label{fig:m3c}
    \end{subfigure}

    \caption{ Correlation graphs and discovered clusters.}\label{fig:enrichment}
\end{figure*}

Expected output m1 & m1c in first row, m2 & m2c in second row, m3 &m3c in third row. I want to add space between each row. However, with above code I could see space between row 2 and row 3 only. Can someone help me to resolve this issue.