In a new file Master Page, I used Type> Insert Special Character> Page number. I've used InDesign for years and never encountered this! (i'm in the Cloud)
I get 1.0... I've looked everywhere, but can't find a clear solution. In Layout> Numbering and Section Options are greyed out, so I cannot format...
What is the name of your master?
Ah! Therein lies the problem. I placed a decimal in the Master Prefix. Thanks for the insight!