if you are having problems check the version you are using. The docs to old (2.x.x) version stay here
Simple money mask use a semver (semantic version) please read the docs equivalent to your version.
First, install it.
npm i simple-mask-money --saveOr use direct of github release
<script src="https://github.com/codermarcos/simple-mask-money/releases/download/<RELEASE_VERSION_HERE>/simple-mask-money.js"></script>remember change <RELEASE_VERSION_HERE> by the last version
Read the read the docs equivalent to your version and choose your implementation: