While we are Migrating data of order deferred line from RR module to subscription billing & that single order have multiple order lines, currently the data importing is failed due to duplicate line error because single order have multiple line.

To overcome problem this my suggestion is that while importing data subscription billing deferred line table entity considered only deferred schedule number for duplication check, if we add line number in that entity & while we are importing data it will consider line number as well with deferred schedule number for checking the duplicates..