Paid restitution will not block the transfer. Once the financial obligation is satisfied, that is no longer a barrier to release or to transferring supervision to another state.
What does have to happen is a formal process between the two states before he can go home to Alabama. Interstate supervision transfers are governed by the Interstate Compact for Adult Offender Supervision, which is an agreement between all 50 states that establishes how parolees and probationers can move between states while remaining under supervision. California cannot simply release him to Alabama without Alabama agreeing to accept supervision of his case.
The process works like this. California initiates a transfer request through the compact. Alabama then investigates whether the transfer serves the public interest, which involves verifying that he has a legitimate residence to go to, that the community is appropriate, and that Alabama's supervision resources can handle the case. Alabama has the authority to accept or reject the transfer request based on their assessment.
If Alabama approves the transfer, he reports to an Alabama parole or probation officer rather than a California one. If Alabama rejects it, he would need to remain in California for the duration of his supervision unless another acceptable transfer location is identified.
The key factors that help Alabama say yes are a verified stable address with a family member or approved residence, the absence of any prohibitions tied to the conviction that would make the proposed address unsuitable, and a clean supervision record that makes him a low risk transfer candidate.
His California parole or probation officer initiates this process, so the conversation about transferring supervision should start there.