AutoID Subitems let you configure an auto increment ID with a preceding text, a starting number and a minimal number of digits in subitems. The AutoID is stored in the specified text column or the Subitems’s name (leftmost) column.
When added to the board the recipe can be configured with the sentence:
When an sub-item is created, generate an auto-increment ID, starting with this number using this format and minimum number of digits in this column.
The text column specified in this column will be automatically populated with an ID which is preceded by the specified (this format) and starts with this number. The number of digits variable specifies the minimum number of digits. An ID can look like this INV-0100. By specifying fields in the this format box you can reference the content of columns in both the parent item and the sub-item, see the detail document for a full description of the available fields.
It is highly recommended to lock the ID column by clicking the down arrow and choose Column Permissions > Restrict column edit. Alternatively you can use a special read-only column which can be created with a recipe provided in the app.