isValidGstin static method
Validates Indian GSTIN (GST Identification Number)
Implementation
static bool isValidGstin(String gstin) {
final gstinRegex = RegExp(r'^[0-9]{2}[A-Z]{5}[0-9]{4}[A-Z]{1}[1-9A-Z]{1}Z[0-9A-Z]{1}$');
return gstinRegex.hasMatch(gstin.toUpperCase());
}