[Tex/LaTex] \footcite command generates errors

Question

I am trying to use BibTeX to generate references for a paper. I can just about get it to cite as I want using the \cite command. But I would like the references to be below the text. I have attempted to use the \footcite command, but this produces the following error "! Undefined control sequence. l.74 …Generic text.\footcite
[{pp.~20-1.}]{ref… The control sequence at the end of the top line of your error message was never \def'ed. If you have misspelled it (e.g., \hobx'), typeI' and the correct spelling (e.g., `I\hbox'). Otherwise just continue, and I'll forget about whatever was undefined."

In abbreviated form my code is like this:

\documentclass[11pt]{article}
\usepackage{fullpage}  
\renewcommand{\baselinestretch}{1.5}
\usepackage[hang]{footmisc}
\setlength\footnotemargin{10pt}
\usepackage[natbibapa]{apacite}
\bibliographystyle{apacite}
\begin{document}
Generic text.\footcite{ref}
\bibliography{QPbib}
\end{document}

Bib is like this:

@article{ref,
Author = {Garth Marenghi},
Date-Added = {2017-09-07 18:04:40 +0000},
Date-Modified = {2017-09-07 18:05:14 +0000},
Journal = {Expertise},
Number = {4},
Pages = {208},
Title = {Darkplace},
Volume = {38},
Year = {1988}}

(I have included the footnote margin commands in case these are part of what is generating the problem. Likewise for \baselinestretch. I was originally using the setspace package but this generated errors that I will be asking about in a separate question.)

Thank you for your help and apologies for my no doubt callow errors.

Answer 1

Here's one possible way you might define \footcite. If you want something different, just substitute the relevant citation command from apacite.

\begin{filecontents}{\jobname.bib}
@article{ref,
Author = {Garth Marenghi},
Date-Added = {2017-09-07 18:04:40 +0000},
Date-Modified = {2017-09-07 18:05:14 +0000},
Journal = {Expertise},
Number = {4},
Pages = {208},
Title = {Darkplace},
Volume = {38},
Year = {1988}}
\end{filecontents}
\documentclass[11pt]{article}
\usepackage{xparse}
\usepackage{fullpage}
\renewcommand{\baselinestretch}{1.5}
\usepackage[hang]{footmisc}
\setlength\footnotemargin{10pt}
\usepackage[natbibapa]{apacite}
\bibliographystyle{apacite}
\NewDocumentCommand\footcite{ O{} O{} m }{%
  \footnote{\citet[#1][#2]{#3}.}%
}
\begin{document}
Generic text.\footcite{ref}
\bibliography{\jobname}
\end{document}