When you make a sale in your store, it will typically have one or more purchase orders associated with it, and it's considered best practice to keep these named differently as they are separate documents with different purpose.
In order to differentiate between a sales order and purchase order, Duoplane will always issue a new name for purchase orders when created. By default, Duoplane adds a suffix -1, -2, -3, etc to each PO created for the sales order, but another setting can be enabled that gives POs their own numbering system independent from the sales order. See the two examples below:
Order number with suffix
Sales order number: PT23456
POs created: PT23456-1, PT23456-2, PT23456-3
Numeric:
Sales order number: PT23456
POs created: 553, 554, 555
Note: above the POs for the numeric example are simply picking up off of whatever last PO number was created by the Duoplane system, which in this case was 552.
To change this setting, in your Duopane retailer account navigate to Main Menu > Settings > Order Processing and use the dropdown menu for "PO numbering"