You cannot log in to myIR because the GST Number in Company Options does not match the Employer IRD Number in myIR.
There are a number of possible solutions:
If this is the first time you are payday filing, check that the GST Number in Company Options matches your Employer IRD Number registered with IR.
You may be trying to log in to the wrong myIR account (such as a different company or your personal myIR account). Try logging in to the correct account.
Have the owner of the IR account verify that that the myIR login being used has the correct rights. In myIR go to My Business, Logon, Manage Access and check the access rights for the account.