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You can sponsor someone an SBI share for 1 Hive. If you sponsor someone the sponsor gets 1 share and the person sponsored get 1 share. In order to sponsor someone you send 1 Hive (or whatever amount of Hive ) to @steembasicincome and write the sponsors Hive name in the memo box. Hive basic income will do the rest. I am not sure if you can convert SBI to Hive. You may have to contact them on Discord. But you will get the amount back in post upvotes after a while anyway so people don't really do this.

Conversion of SBI back into Hive is subject to our refund policy, which is intentionally restrictive to prevent abuse.

In most cases it is better for the person to find somebody that will purchase their subscription units (the going rate is usually ~ 0.50 HIVE, since enrollment is 1 HIVE but creates 2 units - one for sponsor and 1 for sponsee).