\subcaption does not work

Question

I am using the following code to list 3 figures in one line. It is working well and showing the figure if I remove the \subcaption for each figure. However, when I include the (\subcaption)s, it shows the figure with the subcaptions but with error shown in the image below. Any suggestion(s)?

\begin{figure}[H]
    %A
    \centering
    \begin{minipage}[t]{\dimexpr.355\textwidth-1em} % 0.335 represents the horizontal spacing
        \centering
        \includegraphics[width=\textwidth]{Fig14_VOL1_Annotated}
        \subcaption{ CA $ < \ang{90}$}
        \label{Fig14:A}
    \end{minipage}\hfill
    %B
    \begin{minipage}[t]{\dimexpr.355\textwidth-1em}
        \centering
        \includegraphics[width=\textwidth]{Fig14_volumegreater90Annotated}  
        \subcaption{CA $ > \ang{90}$}
        \label{Fig14:B}
    \end{minipage}\hfill
    %C
    \begin{minipage}[t]{\dimexpr.355\textwidth-1em}
        \centering
        \includegraphics[width=\textwidth]{Fig14_vmiddlev1withannotation}
         \subcaption{CA $=\ang{90}$}
        \label{Fig14:C}
    \end{minipage}\hfill
    \caption{Volume and contact angle calculations according to CA value }
    \label{Fig.14}
\end{figure} 

Answer 1

Try the following:

\documentclass[12pt]{article}
\usepackage{graphicx,subcaption,mwe}
\usepackage{amsmath}
\begin{document}
\begin{figure}[htb]
    \begin{minipage}[t]{0.2\textwidth}
    \centering
    \includegraphics[width=1cm]{example-image-A}
    \subcaption{CA1}
    \label{Fig14:a}
    \end{minipage}\hfill
    \begin{minipage}[t]{0.2\textwidth}
    \centering
    \includegraphics[width=1cm]{example-image-B}
    \subcaption{CA2}
    \label{Fig14:b}
    \end{minipage}\hfill
    \begin{minipage}[t]{0.2\textwidth}
    \centering
    \includegraphics[width=1cm]{example-image-C}
    \subcaption{CA3}
    \label{Fig14:c}
    \end{minipage}
\end{figure} 
\end{document}