First, we can make the length field required and set the validation to be greater than 0.
The second solution involves allowing the admin to add a prefix or suffix, with or without specifying a length.
To implement this, we need to make changes in the following file:
Packages > Webkul > Sales > src > Generators > Sequencer.php
In the generate method, modify the condition to:
if ($this->prefix || $this->suffix) in line number 113