Error 43 with \setmainlanguage

[WelliSolutions]

I get the following error and I don't know what I'm doing wrong. I'm just trying to compile the default invoice

Error producing PDF.
! Argument of \str_uppercase:n has an extra }.
<inserted text>
                \par
l.61 \setmainlanguage{}

make: *** [makefile:6: output.pdf] Error 43

I wonder a bit why it says line 61, because \setmainlanguage is on line 69 in template.tex

[sbwiecko]

I believe the error comes from the engine, try using xelatex, as proposed in #27 (comment)