KLAN

I guess i got a problem:
I did an account in sedo.com to try to sell my domain (it is merely a try to look how sedo works). But when i tried to put my domain on auction section they told me that for them my domain has not been registered.
I checked on whois and it results already registered, I also have the invoice that attest i bought it (besides all e-mails with order confirmation and everything).
Now, that's what I said to sedo's staff and they asked me to send them the invoice that attest I am the owner.
what should i do ? can I have confidence sending them the invoice ? (I know this question could seem patetic but I'm not used to have confidence easily)
thx for any advise