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# Key Migrate Parameters

Be certain to include a `MigrationTransaction` reflecting the most-recent subscription billing attempt in your first `migrate` call for a given AutoBill. This `MigrationTransaction`, and the `nextPeriodStartDate` will be used to reconstruct the billing schedule for the AutoBill. Supplemental calls to `AutoBill.migrate` may be made to back-fill historical data for a given AutoBill.

**Note:** Subsequent calls to `AutoBill.modify` will not result in modifications to the AutoBill (only the `MigrationTransactions` will be processed to create historic Transaction information). Also note that Vindicia allows only one recurring Transaction to be provided for each billing period in a subscription's billing history.

**Parent topic:**[Importing AutoBills from other Billing Systems to Subscribe](../topics/Importing_AutoBills_from)


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