This can occur either when an address is set to hidden or when Google Maps has trouble identifying the street address.
First, check whether your address is hidden by clicking Edit on your listing within your account and noting the "Hide my street address and just display the suburb" option. If this is checked and you no longer wish to hide the address simply uncheck the option and click Save. The update will reflect on all sites within an hour.
If this is not checked or you wish to leave it checked but still display a map you will need to supply us with the latitude and longitude of your property.
To get the lat/long, please proceed to https://www.google.com/maps and locate your property. Once you click it you will receive the latitudinal and longitudinal co-ordinates (similar to 30*39'00.5"S 152*59'44.9"E -30.650134, 152.995809). Please email these to firstname.lastname@example.org along with your listing address and we will have the map updated to reflect the supplied coordinates within 24 hours.