You cannot see buckets created using a Storj DCS account that you did not create from inside the IX-Systems software through their signup link. TrueNAS is displaying only buckets which have a specific attribution metadata (indicating they were created/used by IX ) while regular Storj accounts do not have these metadata for the IX buckets by default.
However, if you file a support ticket and share with us what is the name of the project and bucket which you want to be able to access from TrueNAS/IX-Systems, we will be able to have our prod owner add an attribution tag to that bucket so that it will become visible for you.