You will need to activate the Web Services in your Synology DS713+ for many of the services offered, like CloudStation, WordPress, AudioStation and many more.
Here are the steps on how to do this:
2. Access the Web Services icon in the “Network Services” panel:
3. Click “Enable web station” in the web services control panel and “Enable MySQL” and click apply:
And that’s it, you don’t need to do anything else. You can now install wordpress in your nas.