"Contact Details" In case of a tax agent, it is used for tax forms, as the ATO requires an agent's name. , Also, it is for e-signing forms/SPFR by agents.
General Contact Details. In this case we are filling the details for a company and so the signatory must be noted.
"Settings > Contact Details" for Individual entity -
"Settings > Contact Details" for Company, Partnership, SMSF, Trust, and Partnership.
Note that Primary Contact/Signatory is the person who receives, signs the tax return.
For FOREIGN addresses State and Postcode are not required on tax forms (also not required to fill under Settings>Contact details). ATO requirement is that postcode is maximum 4 characters long. Workaround for this kind of issue is to left empty the said fields (State and Postcode) and add this either Line 1 or 2.