I had another look and was able to obtain full version with luckypatcher.
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Install from Play Store
In luckypatcher, find RBC and select 'menu of patches' then choose 'apk rebuilt for InApp and LVL emulation'
Check off 'remove integrity check and signature verification' then hit 'Rebuild The App' button.
Once it finishes, select 'Go To File' button, then 'Uninstall and reinstall'
Select 'Yes' button, then select 'uninstall'
Then select 'Install' and once done, 'Open'
Once at the chess board, select 'menu' button at the top of the screen, then 'quit to main menu'
Hit the green '15' to begin purchase, then check both boxes in the pop up window that appears, then hit 'Yes'
Fully close RBC (remove from recent app list) and return to luckypatcher.
Find RBC and select 'purchases sorter'
Press the coin graphics on the right side to show as yellow, then select 'launch' button.
RBC should show window thanking you for purchase. Undos can be purchased the same way (hit the green 18.)
Enjoy the game!
Please post here if any issues and I'll try to help. Hopefully I got all the steps listed correctly...