It sounds like this may be an app developer issue. These are often based around making your account secure when accessing the site data. Hopefully someone from OVO will pick up on this and be able to give an answer and when a resolution will be in place.
Hey @Pilgrim2,
I’ve reached out to the team and asked for their advice. I’ll come back and update you when I get an answer 
Hi @Pilgrim2,
The team have replied saying that due to the RTS (Radio Tele Switch) turn off, we’re unfortunately not actively looking to give complex metered customers access to the app. As soon as it’s possible, those with complex meters would be offered to swap to a smart meter, once the swap is complete they’d then be able to access the app.
I apologise about any inconvenience caused. We’ll update all related threads as soon as we have any further updates on this.