Reference to a hint of the current exercise when using xsim

Question

I want to print on the margin paragraph a \pageref to the hint of the current exercise.

This is a follow up to a previous question of mine which I rely on, but for some reason my code doesn't work.

I don't understand why I get the error

LaTeX Warning: Reference `hint:1' on page 1 undefined on input line XX.

although I do create a label for each hint, by using this line of code:

\ForEachUsedExerciseByType{\GetExercisePropertyT{hint}{\label{hint:#2}}}

(copied from the linked answer). I expect this line of code to create a label hint:1 for exercise with ID 1, and label hint:2 for exercise with ID 2 etc.

The complete code is:

% !TEX TS-program = xelatex
\synctex=0
\documentclass[openany,oneside]{book}
\usepackage{xsim,geometry,hyperref}
\geometry{left=20mm,textwidth=130mm,marginparsep=10mm,marginparwidth=50mm}

\xsimsetup{
  exercise/name={Question},
  exercises/name={Questions},
  solution/name={Solution},
  exercise/within = chapter,
  exercise/template=myTemplate,
  solution/template =myTemplate ,
}

\DeclareExerciseProperty{hint}
\newcommand\hint[1]{\SetExerciseProperty{hint}{#1}}

\ForEachUsedExerciseByType{\GetExercisePropertyT{hint}{\label{hint:##2}}} %<<-- Apparently creates a label

\DeclareExerciseEnvironmentTemplate{myTemplate}
{%
\IfInsideSolutionTF
    {\label{sol:\ExerciseID}}
    {\label{ex:\ExerciseID}}%
{\par\normalfont\bfseries\GetExerciseName~\GetExerciseProperty{counter}~\GetExercisePropertyT{subtitle}{{(\PropertyValue)}}\newline}
\IfInsideSolutionF{\marginpar{%
\IfExercisePropertySetT{hint}{hint on page \pageref{hint:\ExerciseID}} %<<-- This label is undefined
}}
}
{\par
}

\begin{document}
\chapter{Euclidean Geometry}
Questions for this week:
\section{Questions}

\begin{exercise}
Prove Pythagoras' theorem
\hint{The sum of the angles in a triangle is equal to 180 degrees.}
\end{exercise}
\begin{solution}
The theorem can be proved algebraically\ldots
\end{solution}

\begin{exercise}[subtitle={Proof of Thales's Theorem}]
Prove Thales's theorem.
\hint{the base angles of an isosceles triangle are equal. }
\end{exercise}

\begin{solution}
Let $\alpha=\angle BAO$ and $\beta=\angle OBC$\ldots
\end{solution}

\begin{exercise}
Prove the angle bisector theorem.
% no hint for this exercise
\end{exercise}

\begin{solution}
Consider triangles $ABD$ and $ACD$\ldots
\end{solution}


\section*{Hints}
\ForEachUsedExerciseByType{%
{\normalfont\bfseries Hint #3\par}
\ExercisePropertyGet{#1}{#2}{hint}\par%
}
\section*{Solutions}
\printsolutions[headings=false]
\end{document}

Answer 1

A label assigns to key the number of the current sectional unit, and no sectional unit is in the vicinity of your command where you expect to create a label.

You have to append the \label{hint:#1} into an item of a list environment such as description, as done in the answer you linked to.