benecaster_migration_completion_link

Filters the per-person link the migration emails carry — the one that signs a migrated subscriber in and takes them to sign up. By default it is your site’s address with two query arguments: one identifying the person, one naming the tier they were mapped to.

The link signs its holder in, so treat it as a credential. Never log it, and never send it anywhere but to the person it belongs to.

This changes the link, not where it lands. To send people somewhere else, use benecaster_migration_checkout_url. A link that loses its identifying argument identifies nobody.

Only paying members have one. A free member is never asked to pay, so the filter never runs for them.