Requirements to meet for it to be instant and free:
To transfer between your accounts instantly and for free, they would need to be linked together first. To get them linked, all you need to do is complete the verification on both accounts using the same identification document. After your accounts are approved, they will be automatically linked by the system.
Note: If your sub account has referral link applied to it, it will be removed once the accounts are linked
How do I know if my accounts are linked?
If you've already verified both accounts and you're not sure whether they have been linked, you can reach out to Support to check on it for you. Linked accounts are not visible through the site at the moment.
How do I submit the transfer?
The process is the same as any withdrawal - just submit the request on the Wallet page from one account to the deposit address of the other account. While you're asked to enter the minimum fee amount, you will not be charged.
How long will it take to receive the transfer?
After you've submitted and confirmed your withdrawal request, you should see it in your other account right away as the transfer instantaneously happens off-chain.