As Bernard said in his comment, the syntax for labels has changed since version 1.0 of package tasks
.
If you have a version older than 1.0 but at least 0.9 or newer, for example, if you're using Overleaf, which has
tasks.sty 2016/08/13 v0.12 Horizontalcolumnedlists (CN),
you should use counter-format={<counter specs>}
.
This option is now deprecated, it set a custom label in a peculiar way. The letters tsk
are replaced with the task-counter. An optional argument directly following these letters specifies the counter format: 1
: \arabic
, a
: \alph
, A
: \Alph
, r
:
\roman
and R
: \Roman
.
You can find the old documentation of the package in its repository on GitHub.
This works on Overleaf, I hope it works also for you:
\documentclass{article}
\usepackage{tasks}
\begin{document}
\begin{tasks}[counter-format=(tsk[1]), label-width=4em]
\task 1
\task 2
\task 1
\task 3
\task 4
\end{tasks}
\end{document}

\usepackage{tasks}
? This works without problems: dpaste.com/3YHZ7NP (expires in 10 days)