QB Issue Resolution:

You can run something like Parallels that will allow you to run the Windows version on a Mac, or you will need to buy the Mac version.

http://www.parallels.com/landingpage/pd/general/?utm_source=bing&utm_medium=cpc

Resolution for Issue 'When changing from windows to Mac do I have to buy a new license' available: Yes (Solved).
Source: Intuit Community forum.

When changing from windows to Mac do I have to buy a new license: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

Support for License
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Error Recovery for License [Canada]
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