Please check if the installed version of MAXQDA matches your license version. For example, you need to enter a MAXQDA 2018 license to unlock an MAXQDA 2018 installation. If the license is for MAXQDA 12, the license cannot be used to unlock an installation of MAXQDA 2018.
Please also check your serial number for typing errors.
If you still receive this message, please get in contact with our support team. Our technical support team can be contacted through this form: https://www.maxqda.com/support/onlinesupport