Can I link my existing MockFlow.com account with Atlassian JIRA / Confluence integrations ?

Due to Atlassian license restrictions, your existing account / license at MockFlow.com account cannot be merged or linked to MockFlow integrations with Atlassian JIRA or Confluence.

License note

Atlassian integrations and accounts created at MockFlow.com are separate from one another and requires a specific license.

This is due to the following reasons:

MockFlow integrations with Atlassian requires a separate license to be purchased and assigned based on your user count already available in your Atlassian account.
A single MockFlow Team account is automatically created and linked with your Atlassian company (domain) account. This provides seemless sharing and opening of MockFlow projects from within Atlassian JIRA/confluence without additional login.

Is there a way to copy projects between Atlassian integrations and MockFlow.com account ?

You can try following the steps listed here - https://support.mockflow.com/article/86-how-copy-paste-between-wireframe-projects