Issue Summary

This is reproducible on Data Center: yes

Steps to Reproduce

1. In Jira On-Prem, generate a Personal Access Token for your Admin Account
2. Create a CSV file that references Jira Cloud Issues, and Attachments from your Jira on-prem environment

issue key, Summary, Attachment
BC-3,password-update3,Bandit-5;https://admin:*access-token*@*jira-on-prem-url/jira/secure/attachment/10000/Bandit.png 

1. In Jira Cloud navigate to "External System Import"
2. Select CSV
3. Select your File
4. Map the fields (ie: attachment > attachment)
5. Upload the file

Expected Results

The attachment noted in the CSV file is uploaded to the Issue in the CSV file

Actual Results

The attachment is not uploaded to the issue in Jira cloud

The below exception is thrown in the Detailed Import Log in Jira Cloud

 WARN - An exception occurred dealing with attachment 'https://admin:*access-token*@*jira-on-prem-url/jira/secure/attachment/10000/Bandit.png '. 

Workaround

Instead of using a Personal Access Token, use your users password. Its recommended to reset your credentials after the import has been completed.