If you haven't registered yet and want to apply for a patent on paper now, this column is unnecessary.
It is suggested that if you apply for a large number of patents, you should register an electronic account first, and then all related operations will be done through the CPC client, which will save time and effort, otherwise all documents will be registered and mailed, which is very troublesome and takes a long time.
In addition, I looked at the request and there was no user code column. Did you get it directly through the cpc client?