<h1>Transitional credit in TRAN-1 requires prior inclusion of earlier registrations in enrolment to avoid validation errors.</h1> To claim transitional credit in TRAN-1 for legacy Central Excise, Service Tax and VAT registrations, taxpayers must first add those legacy registration numbers to their GST enrolment via the non-core amendment facility because the TRAN-1 application validates legacy registration numbers against enrolment data; failure to match causes a 'processed with error' status. When filing the non-core amendment, omit special characters in registration numbers, avoid duplicate contact details for stakeholders, use updated Service Accounting Codes, and place STD codes in the correct telephone field to ensure successful TRAN-1 submission.