Yes, there was a bug in the Go Pricing plugin which caused that error in WordPress v5.3. The plugin author has now fixed the bug and we have included the updated plugin in the theme update we have just uploaded to ThemeForest. That update should be available in your ThemeForest downloads area real soon now. (If you have enabled the option in your ThemeForest downloads area, you will receive an email when the new theme update is available.) Thanks.