Summary
When trying to view a VisualForce page, an "Insufficient Priveleges" error is shown, so user can't see the related Jira Issues, and can't create or associate issues either.
Environment
Jira Cloud
Salesforce
Cause
This is usually because the current user has not been granted access.
Resolution
In order to grant this access:
In Salesforce go to the Setup > Custom Code > VisualForce Pages.
Click on the Security link, and you will be sent to the Page Level Security Page.
Select the Current User Profile from the Left side and click the Add button and click Save.
Now you have given Page Level Security to the Profile Added.