This error occurs when a customer attempts to link their version of the 24x7 app with an account on which they do not have the required level of access. This generally occurs when the overall account ("customer accoun" in Telstra jargon) is in someone else's name.
About ten years ago Telstra did away with so-called "joint accounts" and enacted a system where by there is one over all account holder, who could then nominate people with varying degrees of access. I haven't been told officially, but I suspect this is a result of the divorce rate increasing, Telstra issuing a bill and the joint account holders pointing at each other going "chase them!"
The solution is to get the account holder to get your access upgraded to "Full Authority" assuming they are willing to provide you with that. In the event that they are not, this is not something that can be fixed.
If the Customer Account (to use the jargon) is in your name (the name that appears on the bill isn't much of a clue I'm afraid, this can be edited to say almost whatever you like) this is something the App Support team will need to check out, and they can be reached here: https://tel.st/zxrgq.