As hilldweller stated the ASX is the primary stock exchange.
ISX Cross Listed on the FSE in June 2017. Below is a link to the ASX announcement:
https://www.asx.com.au/asxpdf/20170620/pdf/43k1xgl54zdb35.pdf
Cross-listing is the listing of a company's common shares on a different exchange than its primary and original stock exchange.
https://www.investopedia.com/terms/c/cross-listing.asp
Cross-listing (or multi-listing, or interlisting) of shares is when a firm lists its equity shares on one or more foreign stock exchange in addition to its domestic exchange.
https://en.wikipedia.org/wiki/Cross_listing
