We have multiple 3CX instances hosted in AWS, we are trying to increase the Voicemail Duration but not able to find "MAXVOICEMAILDURATION" option under settings--> parameters to change it there.
As per our guide https://www.3cx.com/blog/docs/maximum-duration-voicemail/, if the parameter does not exist, you will have to add it. Then restart the "3CX PhoneSystem 01 IVR Server" service in order for the change to take effect.