Shipping 2 items in same package with one tracking number..How?

[log-cabin-antiques]

This has got to be simple but I can't figure it out. Buyer buys 2 items from my store, pays for both immediately and asks to combine shipping. In my ebay it shows as 2 sales with no way that I can see to combine them together where one tracking number covers both. What am i missing??

[discountcombustion2]

I have tried this and it gives me error message that that tracking number is already being used.....any way around that?