Hi @mat4 ,
OK, then you can generate the number automatically using below formula, and use it when submitting the collection:
Set(varPO, Concat(Add(First(Split(Last(SPlist).'PO Number'),"/"),1),"/WESS"));
Patch(SPlist, ForAll(collection, {'PO Number': varPO, Quantity: ThisRecord.Quantity}))
The variable is getting the PO Number from the last item of your list, split the value with / to get the number, add 1 to it and concatenate with "/WESS" to generate the new PO Number. Then this variable is used in the Patch function to update the value to list.
Best regards,