Hey @Ron, Google allows developers to limit the number of devices that a paid app can be installed on per account, however, usually that number is unlimited.
When you go to the Play Store on your tablet, if you've paid for an app on your phone, you should see ''install'' (where the price normally is), not ''installed'', as that app has not been installed on your tablet yet. See screenshots below of Link Bubble Pro, which I've paid for on my smartphone and now looked up in the Play Store on my tablet. You can see it's got the ''tick'' meaning I've already installed/paid for it, but I can still install it again.
Perhaps you could try deleting your Google account and adding it again, or clearing the Play Store data/cache and trying again.