On 1 April 2027 your invoice series can start again at 1. Here is what Rule 46 actually requires,
Rule 46(b) requires invoice numbers to be unique within a financial year, so a reset on 1 April is allowed but not compulsory; continuing the sequence is also compliant.
A financial year prefix such as INV/27-28/ makes every number self-identifying and keeps a reset from producing duplicates across years.
Whatever you choose must fit in 16 characters including the prefix, use only letters, numbers, hyphen and slash, and run consecutively.
Reset every document type that has its own series (credit notes, debit notes, delivery challans, receipt vouchers), and report the new ranges in GSTR-1 Table 13 for April.
No. Rule 46(b) requires the serial number to be unique for a financial year and consecutive.
The full guide has the formats, the deadlines and the worked examples.