Once you purchase a subscription to WineRatings+, you are able to install it on multiple devices you own -- as long as you are doing the installations all from a single
Apple account associated with those devices.
Some people use different Apple IDs (usually an email address) for different devices, particularly if they use one device for work and another for personal use. If you previously downloaded the app from a different Apple ID than the one you have now, that is likely the cause of the difficulty you are now experiencing.
If this is your first time subscribing to WineRatings+, had you previously installed an earlier version of the free download under a different ID?
If this is your first time downloading WineRatings+, had you previously
installed VintageChart+ from a different ID? WineRatings+ replaces that app as an update,
so you may be required to use the same ID to run this replacement update.
check which Apple ID you are using on each device, go to Settings, then
to iTunes & App Stores. Your Apple ID will be at the top. If you
have multiple IDs, you can sign out of that one and switch to the one you used to originally purchase the app.