  Given a $C^*$-dynamical system $(A,G,\alpha)$, with $G$ a discrete group,
Schur $A$-multipliers and Herz--Schur $(A,G,\alpha)$-multipliers are used to
implement approximation properties, namely exactness and the strong operator
approximation property (SOAP), of $A \rtimes_{\alpha , r} G$. The resulting
characterisations of exactness and SOAP of $A \rtimes_{\alpha , r} G$
generalise the corresponding statements for the reduced group $C^*$-algebra.
