Special GST migration procedure lets taxpayers with provisional IDs obtain GSTIN by following prescribed application and mapping steps. A special migration procedure allows taxpayers who hold only a Provisional Identification Number after incomplete REG-26 filing to apply in FORM GST REG-01 on the common portal, obtain a new GSTIN, ARN and access token, submit new and old identifiers to GSTN for mapping, and then use the old PID for first-time login to generate the registration certificate; registration is deemed effective from the stated retrospective date.