My M2e Pro will not work with Amazon, Rakuten and eBay when I have the CSF (ConfigServer Security & Firewall) turned on. I have looked for answers what to open for M2e Pro to work, but can't find an answer. M2e Pro just reports "Server connection is failed. Please try again later. "
Not understanding how M2e Pro connects was what was leading to the problem. M2e Pro connects to it's own servers I believe in Germany to process data. There is no direct connection to say, Amazon, eBay or Rakuten. So what I had done was blocked countries in CSF, one of the being Germany because I was getting hacked. The IP for M2e Pro I believe in is in Germany. I had an IP number but I can't find it and did not annotate it in my Allow. You can send a support request to get it.
After removing the country code everything started to work again.
Now I only have China and Russia blocked as they attack daily.
In cPanel/WHM select Plugins >> ConfigServer Security & Firewall >> Firewall Configuration.
From the top drop-down menu select [Country Code Lists and Settings] in the CC_DENY = [ ] put in or remove country codes. Mine are [CN,RU]. Don't forget to restart CSF.
Note only put in 2 characters as 3 will not work.
You may need to allow in other places?
I am posting this from my poor memory about the servers. You may need to check with M2ePro on what to allow.