Unable to upload attachments

Hi Experts,

We are planning to migrate the records from a legacy system to the RTC. Below are the things we are looking into.
1. Migrate the user information
2. Migrate the records (Work Items)
3. Migrate the attachments associated to each work item.

We are not able to do the 3rd point (i.e. Not able to migrate the attachments). We followed the below approach:
-> created the import CSV and gave the attachment path into the CSV. During import, the tool is not throwing any error message and also the attachments is not getting associated to the work items.
-> In some community, we saw we can import the attachments from the Bugzilla format. We tried to create the Bugzilla import file manually and tried to uplaod the attachments. But that is also not working.

Please let us know if there is any way to import the attachments to the RTC work items. If yes, let us know the step by step procedure to do the same.

Regards,
Sharath TS