Solution 1ModSec
Check to make sure your host does not have a mod_security (ModSec) rule that gets tripped. On some servers running allot of database commands or even unzipping a file cantrigger a mod_security black list rule. This simply means the host your on is blocking your IP from doing certain operations. This can easily be solved by contactingyour host and making sure they don’t have a mod_security rule that is blocking you from accessing the installer properly.

Solution 23rd Party Services
There are a few issues around WordFence and Cloudflare that can cause these codes. See the FAQ below for details:

• What can I try for 502/503/504 Gateway issues during the build?

Solution 3DYI
During the install process it is possible that your host might automatically lay-down a .htaccess file. Typically Duplicator works best if no .htaccess files are presentdurning the install process as some of the directives in the file can cause conflicts. If your wanting to try and resolve the issue your-self without your hosts assistance thencheck out the article below:

• How to Fix 504 Gateway Timeout Error in WordPress

Solution 4Permissions
A 500 error in Step 1 processing on Duplicator Lite can sometimes be due to a timeout during zip extraction or on Duplicator Lite or Pro when file permissions are being set.To get around this, first do a Manual Extraction then uncheck the Files and Directorypermissions boxes on Step 1 of the installer.

Solution 5Cloudflare
If you’re using Cloudflare the below settings may help

1. Log in to Cloudflare
2. From Overview Page click “Advanced” > Click “Pause”
3. Run installer deployment
4. Turn Cloudflare back on

Solution 1In the event the host you are on has issues with AJAX callbacks the best solution is run a manual install. For a step by step run of this processsee the FAQ item How do I do a ‘Manual Extraction’ or run installer without Zip enabled?.