User should select the appropriate PAYG Option. It's not possible to report both the instalment amount and the varied amount. It says -  OR IF varying T7, complete T8,T9,T4.

If issues persist, check:

- If the form IAS is past due? you will not be vary the instalment amount, please contact ATO in such case. 

In case ATO is not able to help, please adjust it at year end.