This is the exact same issue I am having. We booked a cruise about a month ago and paid the deposit and every time we try to access the Ocean Ready section we get the same error message.
We can access the Medallion app okay and have booked our dining reservations with no problem but just cannot get any further.
We have tried on several different phones, iPads and even tried the web version but it just won’t work.
We phoned Princess and they too couldn’t gain access and so we have had to email all the info & error messages to their IT department.
Fingers crossed they can sort it out as it appears something somewhere is not working or being recognised as it should be.