ERROR: duplicate key value violates unique constraint "import_ids_pkey"


i’m trying to import my IPB 3.4 forum (200k users, 1.5M posts) into Discourse using ipboard.rb
Importing users went fine, but i encounter below error when importing topics:

**Traceback** (most recent call last):
10: from script/import_scripts/ipboard.rb:1029:in `<main>'
9: from /var/www/discourse/script/import_scripts/base.rb:47:in `perform'
8: from script/import_scripts/ipboard.rb:146:in `execute'
7: from script/import_scripts/ipboard.rb:355:in `import_topics'
6: from /var/www/discourse/script/import_scripts/base.rb:881:in `batches'
5: from /var/www/discourse/script/import_scripts/base.rb:881:in `loop'
4: from /var/www/discourse/script/import_scripts/base.rb:882:in `block in batches'
3: from script/import_scripts/ipboard.rb:377:in `block in import_topics'
2: from /var/www/discourse/script/import_scripts/base.rb:223:in `all_records_exist?'
1: from /usr/local/lib/ruby/gems/2.6.0/gems/rack-mini-profiler-1.1.6/lib/patches/db/pg.rb:56:in `exec'
/usr/local/lib/ruby/gems/2.6.0/gems/rack-mini-profiler-1.1.6/lib/patches/db/pg.rb:56:in `exec': **ERROR: duplicate key value violates unique constraint "import_ids_pkey" (** **PG::UniqueViolation** **)**
**DETAIL: Key (val)=(discussion#50554) already exists.**

The error message is clear, but my question is how can i identify what is the duplicate key ? Where to look ?
At first, i thought it was IPB topic_id = 50554, so I deleted the record and relaunch the import script but I got the same error.
I’m not sure where to look from here…

Thank you