Let’s see why the connection between the LR plugin and the WP plugin is not working. If you get another kind of error which sounds more like a bug and not a connection problem, check 6. Otherwise, continue reading.
Maybe your website is under construction, disabled by a plugin, in maintenance mode, or something that avoids user to login naturally? Make sure your website is normally accessible. Also, make sure that potential plugins that might block external connections are off, at least for this debugging, such as: Coming Soon Page & Maintenance Mode by SeedProd, WP SpamShield.
Before the WP/LR Sync for LR 2.6.0, the plugin was always using XML/RPC, which was not playing well with many hosting services (because of historical security issues in the protocol, even though it has been fixed for a long time now). I therefore recommend you to switch to the latest version of the LR plugin and change the Protocol setting of your Publish Service to REST. Try again, and go to 2 if it is still not working.
If you are really willing to use XML/RPC, have a look here.
Check if /wp-json is available on your install. For example, on my haikyo.org website, this URL is http://haikyo.org/wp-json. Understanding it is not important, but make sure that the “wplr” string is present somewhere in this. If you can’t find “wplr”, check 3. If this return an empty page (or 404), please have a look at 4.
Sounds like not a very clever question, but sometimes that might be that the plugin is disabled 🙂 Can you check your Plugins page in WordPress? If not, enable it and try everything again. Also, there are plugins that can disable other plugins or their functions. Please make sure you try to disable all the plugins and test WP/LR Sync alone (such plugin as Plugin Organizer for example can do that). If nothing helps, go to 5.
The WordPress API needs the .htaccess to be set-up. Sometimes, WordPress doesn’t do it magically and you need to trigger it. Check your Permalink Settings (/wp-admin/options-permalink.php), check Post Name (as long as it is not Plain), Save Changes. Perform the same check as you did at 2. Does it work better? It is better to use permalinks and that keeps your .htaccess to work with dynamic URLs (if you wish to do this manually, with the permalinks off, check here: StackOverflow).
You have to be aware that if ANY other plugin fails or generate an error during the WP/LR Sync process, WP/LR Sync will unfortunately fail too. So you need to check your PHP Error Logs to make sure nothing happens during the WP/LR Sync process. Check it before using WP/LR Sync, perform an action (login, sync, or anything else) and check it again. Did something happen in between? Disabling all the plugins (but keep WP/LR Sync enabled) and try again.
Your PHP error logs are made accessible by your hosting service, if you don’t know where they are, the best is to ask them. You can also try to use such a plugin as Error Log Monitor. If you are willing to learn more about checking errors by yourself, check this: Monitor PHP Errors.
Alternatively, you can also have a look at your WPLRSync.log located in your Documents folder.
Nothing worked? Then, contact me, and add some debugging information about what you found and what you did.
This is not helping? Please go to 5.