I am sorry to hear that your Z7-Pro headphones cannot be used in the Line-In mode, and I want to help.
Please follow the troubleshooting steps below:
1) Clean the AUX cable connector with a small soft brush to remove debris.
2) Clean the AUX port using a eyelashes brush (or similar) soaked in rubbing alcohol.
3) Check if there is any visible damage to the AUX port.
4) Try to use another AUX cable.
Please let me know if any of the mentioned steps above helped.
Additionally, kindly note that high humidity and extreme temperatures can cause the deformation of the device and affect its performance. Please let us know if your headphones were damaged or exposed to extreme temperatures.
If you have some questions, comments, or want us to help you, please click Contact Us. We will be happy to help!