Thank you for the response Phillip.
I have successfully upgraded to v3.5.6 using clean database and imported the JSON file from Configuration Import/Export. However, when performing the "Migrate NoSQL data", i have encountered the below error (see screenshots).
It looks like the my existing database is having issue with the upgraded version since the migrate NoSQL data is getting its source from the old database?
And finally, we have created customized pages/dashboards. Apart from the JSON and Databases migration, what else do we need to import to the upgraded version? Say for example the licenses?
Appreciate the support.