Error 503 when attempting to get Google Base URL

OpenCart 2.0.3.1

Using standard Google Base feed module.

Data Feed URL: http://www.mydomain.com/index.php?route=feed/google_base

Checking it in browser - shows up fine (screen upon screen of XML info), no errors.

Submitting it into Google Merchant Center:

Filename: googlebase.xml
URL: same as in Google Base module.

Trying to do a test fetch - get a 503 Error:

Invalid response code. 1 error.
The remote server returned an invalid response code.
503 http://www.mydomain.com/index.php?route=feed/google_base

Does anyone have advice on this? I would even pay for a solution or an extension.

Thanks in advance!

What is oyur actual domain ?