If the import stalls and fails to respond after a few minutes, or it fails with a simple error message like “Import failed,” You are suffering from PHP configuration limits that are set too low to complete the process. You should contact your web host and ask them to increase those limits to a minimum as follows:
You can verify your PHP configuration limits by installing a simple plugin found here. And you can also check your PHP error logs to see the exact error being returned.
This is a common server/hosting issue. You need to ask your hosting to increase your PHP max_upload_size variable, preferably above 25mbs.
Here is a sample code you can pass onto your hosting:
upload_max_filesize = 64M post_max_size = 64M max_execution_time = 300
WP_Debug is a constant that when enabled will display any PHP errors on the front-end of your site, this is the most useful tool when troubleshooting your site for errors. If disabled and your site has an error you may see a blank screen or content missing on the site but no error message, that makes it nearly impossible to figure out the problem. Personally I keep WP_Debug enabled on all my sites so if I install a new plugin or update a theme I’ll know right away if there are any errors and be able to contact the developer to fix them or fix them myself.
Below are the steps required to enable WP_Debug for your WordPress installation.
define( 'WP_DEBUG', true );