Cannot add multiple subscription items with the same plan

[ianatha]

-----> Migrating subscriptions
       Using subscription sub_[...1...] as the primary subscription
       > Plan: [...2...], Quantity: 1
       
       Adding the following items to the primary subscription
       > Plan: [...2...], Quantity: 1
       > Plan: [...3...], Quantity: 1
       > Plan: [...2...], Quantity: 1
       > Plan: [...2...], Quantity: 4
       > Plan: [...2...], Quantity: 1
       
       Updating primary subscription, prorating other subscriptions
       Added plan [...2...] with quantity 1 to sub_ANxxEdnE3rNFMC

ERROR! Migration unsuccessful
       {"type":"invalid_request_error","message":"Cannot add multiple subscription items with the same plan: [...2...]","param":"plan","request_id":"[...4...]","status":400}