Hello,
If the table is not created correctly you will definitely not be able to perform transactions. This is why the plugin is warning you.
This is an issue that was fixed in a past release. I assume you have already checked that you are installing the latest version.
If that’s the case, I recommend that you drop the two tables and reinstall, this time taking note of any errors in the logs. That’s the only way to know what went wrong. The plugin has been tested with PHP 5.6 and it should work.
Do let me know what you find.
regards