How do I find out my eBay user email address?

[Rich-Allen1976]

I know I use my main Gmail account for buying and selling but for FedEx tracking on an order, it wants my eBay email address?

It says my Gmail wasn't acceptable and it's something at members.ebay.com?

How can I find this out? I just Googled it and it says to go in personal info on my eBay account and I have done but it's not there?

I have used Google.