Transfers a junior account to the account holder now that they have graduated to an adult account.

The caller must be the junior: their token must carry a minor identifier and a guardian email. The account named in the path must belong to that guardian, and the email in the body must match the account's email address. On success the transfer is applied immediately and a confirmation is emailed to the guardian — no acceptance step is involved.

There are a few important requirements in order to use this endpoint:

1. The JWT used in the Authorization: Bearer {access_token} header must represent a junior i.e. must contain both minor_id and guardian_email claims
2. The authenticated user making the API call (JWT above) must have just recently graduated (upgraded) their SSO account from a junior account to an adult account – therefore it is imperative that this endpoint is called straight away after the junior account has been upgraded and before refreshing the access token which will return an adult JWT (without minor_id and guardian_email claims)
3. Validation checks will be performed to ensure the email address in the request body matches the new email address of the graduated (upgraded) SSO account
4. The guardian_email from the JWT claim will be used to validate that the sourceSystemUserId (client ref) has the same email address