This library uses mbelib as one of its source component, which patent notice from https://github.com/szechyjs/mbelib/blob/master/README.md is worth reading:
This source code is provided for educational purposes only. It is a written description of how certain voice encoding/decoding algorythims could be implemented. Executable objects compiled or derived from this package may be covered by one or more patents. Readers are strongly advised to check for any patent restrictions or licencing requirements before compiling or using this source code.
I am not involved in any way with the softmbe installation script or softmbe library, I am just providing easy access to the installation script.
Copy the shell script and paste it to a command line of your machine
wget 'https://fms.komkon.org/OWRX/install-softmbe.sh' && chmod +x ./install-softmbe.sh && sudo ./install-softmbe.sh
The script downloads the 'install-softmbe.sh' script to your machine, makes it executable and executes it with root privileges. If not already root, you will be asked for password for elevated permissions.
See the OWRX+ FAQ for more information
Restart OWRX service
systemctl restart openwebrx
Browse to the OWRX settings page and Feature Check subpage, and check that 'codecserver_ambe' status shows YES
Additionally, digital modes which use AMBE codec should have appeared to the mode selection on the receiver control window: