If you hold a valid LearnDash license and you find yourself unable to activate LearnDash in WordPress, then your current host configuration may prevent the LearnDash plugin from calling home to its license activation servers.
After keying in your license the LearnDash plugin will initiate outgoing HTTPS requests that are used to forward the activation request to LearnDash. These requests will not reach LearnDash activation servers when your hosting environment is blocking outgoing HTTPS requests. This also applies when you move your WordPress site from one system to another.
If you are using CentOS Linux there is a chance that SELinux is preventing LearnDash from being activated. SELinux is a security mechanism that helps keep CentOS secure and is enabled by default. Use the “getenforce” command to verify that SELinux is enabled.
Use the “setsebool” command to allow the webserver and WordPress to initiate HTTPS sessions.
setsebool -P httpd_can_network_connect 1
LearnDash should now activate.