eBay will never explain any restriction.
We cannot see any messages you sent or received because we have no access to your account, but if anyone asked to perhaps come and see an item you are selling before buying unless very strong message sent back that this was not possible until the item was bought and paid from through eBay checkout, could be deemed as the beginnings o an off eBay sale.
If you have received a permanent or indefinite restriction that i a lifetime ban not turning back from that, but if it's a times restriction for example 7 days, then you just need for this time to lapse to be able to sell again.
@kebai5496