.../lib/mongo/operation/result.rb:364:in `raise_operation_failure': [2]: can't have multiple _id fields in one document (on 127.0.0.1:27017, legacy retry, attempt 1) (Mongo::Error::OperationFailure)

require 'bundler/inline'
gemfile do
 source 'https://rubygems.org'
 gem 'mongo'
end
client = Mongo::Client.new(['127.0.0.1:27017'], database: 'PoC_DTM') # Assuming you have a mongo server running on port 27017
db = client.database
collection = db[:fake_collection]
collection.insert_one({ field: 'test', _id: nil }) # => OK
collection.insert_one({ field: 'test', '_id' => nil }) # => KO

...
 def id(doc)
 doc.respond_to?(:id) ? doc.id : (doc['_id'] || doc[:_id])
 end
 def has_id?(doc)
 !!id(doc)
 end
 def ensure_ids(documents)
 @ids = []
 documents.collect do |doc|
 doc_with_id = has_id?(doc) ? doc : doc.merge(_id: id_generator.generate)
 @ids << id(doc_with_id)
 doc_with_id
 end
 end
...