The version you have is not the latest. Platinum parcels were dropped by Aust Post a while ago and taken out of aupost early this year

Please download the latest version from GitHub https://github.com/OldNGreyBMR/aupos...s/tag/2.5.5-07
Don't forget to remove the module and then reinstall the module to install the latest changes and values.
If you set Hide Handling Fees? to No it should have text after the returned value like (Inc $0.00 P & H)).

With the latest version I can track down the error by the line number. When the error occurs, It looks like you are getting an invalid or empty quote back from Aust Post.

Are all of your product weights in kgs?