(This dialog must be opened when Command-Shift-V is pressed)
According to Apple's Pages Keyboard Shortcuts support page, thereThe only possibility here is no command-shift-V nor shift-command-V, so if that exists, it is unpublished.
edit: I've been informed in the comments that itoption key you are using in your key command is an Insert menu itemnot registering.
Possibly helpful to you:
to see the list ofThis could be caused by your fingering technique, your keyboard shortcuts in Pages, choose Help > Pages Keyboard Shortcutsor both. Try using the other option key and see if that mitigates the issue.
From the page linked above:
Paste and match style of destination text..............Option-Shift-Command-V
Possibly helpful:
Also, try checking in System Preferences.app/Keyboard control panel/Keyboard short cuts for any conflictingto see the list of keyboard shortcuts in Pages, choose Help > Pages Keyboard Shortcuts.
This may also be helpful to any experiencing inconsistent keyboard commands