Typically you only allow for transfers between accounts that have the same owner. Think about personal accounts - you would not want your bank to allow me to transfer funds from your account to mine. It's the same with a business - you only link accounts of the same owner - If each LLC has a separate name and TIN, then they are 3 separate entities - different owners on each account. So, even if they are ultimately owned by the same individual(s), they are separate entities.
Hope that helps - Have a Happy Thanksgiving everyone!
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My comments are absolutely no reflection of, nor influenced by, my employer - take them at your own risk.