Where do I find my registration number? MAMP GmbH August 27, 2014 11:16 Updated Open the dialog File/About MAMP PRO, it is shown there. Related articles How do I recover my license key / serial number? I did not receive my invoice? Are updates free of charge? How do I register MAMP PRO for Windows ? I want to revert back to MAMP PRO 4.5.