The Issuer-Tracked Asset type doesn't place any restrictions on the recipient and there is no need for the issuer to register users in advance. Ownership can be taken by anyone who receives the asset to their Blockstream Green Managed Assets account.

Transfers of the asset between Blockstream Green users is tracked by Blockstream AMP using the owner's Blockstream Green Account ID. The issuer can view the account balances for their asset, while the transactions remain private on the Liquid blockchain.

Make sure the receive address is from within your Managed Assets account and not your normal Liquid account.