Combining invoice and datatool to create serial invoices

Question

I want to generate invoices based on a CSV table. My approach looks like this:

\documentclass{letter}
\usepackage{invoice}
\usepackage{datatool}
\address{ABC AG \\
    Nonamestreet 4 \\
    1100 Vienna \\
    bill@example.com}
\date{16. September 2013}
\begin{document}    
\DTLloaddb{bills}{billdata.csv}
\DTLforeach{bills}
{\firstname=firstname}
{\lastname=lastname}
{\caddress=customeraddress}
{\tariffname=tariffname}
{\service=service}
{\rateperunit=rateperunit}
{\unitcount=unitcount}
{
\begin{letter}{\firstname~ \lastname \\ \caddress}
\opening{Invoice}     Dear customer \lastname! This is your current bill.
\begin{invoice}{Euro}{20}
\ProjectTitle{\tariffname}
\Fee{Regular charge} {\rateperunit} {\unitcount}
\end{invoice}
\closing{Best regards, ABC AG}
\end{letter}
\clearpage
}
\end{document}

The CSV file has the following structure:

firstname   lastname    customeraddress tariffname  service rateperunit unitcount
John    Doe Musterstraße 4  Tariff1 Call    0.04    4
...

I then compile the .tex file with PDFLaTeX.

But I'm always getting this error:

! LaTeX Error: Missing \begin{document}.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
...                                              

l.36 \NeedsTeXFormat{LaTeX2e}[
                           1995/12/01]
? 

and

! Emergency stop.
...                                              

l.36 \NeedsTeXFormat{LaTeX2e}[
                              1995/12/01]
You're in trouble here.  Try typing  <return>  to proceed.
If that doesn't work, type  X <return>  to quit.

I am using the texlive package of Ubuntu 13.04, and I also tried that with csvsimple, ending up with the exact same error.

Answer 1

A part for the error that contains the date that is fixed following the comment of @Ulrike Fischer (by substituting \input{fp} with \RequirePackage{fp} into the invoice.sty file), the main error is in the \DTLforeach command. You don't have to add an argument for each field in your .csv file but group them all in the same argument of \DTLforeach.

Also in your .csv file you need to separate your fields with a , and not with spacing.

\documentclass{letter}
\usepackage{invoice}
\usepackage{datatool}
\address{ABC AG \\
    Nonamestreet 4 \\
    1100 Vienna \\
    bill@example.com}
\date{16. September 2013}
\begin{document}    
\DTLloaddb{bills}{billdata.csv}
\DTLforeach{bills}
{\firstname=firstname,
\lastname=lastname,
\caddress=customeraddress,
\tariffname=tariffname,
\service=service,
\rateperunit=rateperunit,
\unitcount=unitcount}
{
\begin{letter}{\firstname~ \lastname \\ \caddress}
\opening{Invoice}     Dear customer \lastname! This is your current bill.
\begin{invoice}{Euro}{20}
\ProjectTitle{\tariffname}
\Fee{Regular charge} {\rateperunit} {\unitcount}
\end{invoice}
\closing{Best regards, ABC AG}
\end{letter}
\clearpage
}
\end{document}