How can I create a unique Order Number when a Google Form is submitted for approval?

Insert a column on your spreadsheet collecting responses and use the arrayformula below to create numbers in sequential order

=ArrayFormula(if(len(A2:A), "Order Number " & ROW( A2:A )-2 + 10 ,""))

1. Insert a column on your spreadsheet that you will used to create unique Order Numbers

2. Submit your Google Form once. 

3. Insert a row above your Form Submission

4. Add your arrayFormula in the row you have inserted, under the column header that will be used to create the Order Number

=ArrayFormula(if(len(A2:A), "Order Number " & ROW( A2:A )-2 + 10 ,""))

5. Start collecting form responses. The Order Number will be generated on your spreadsheet, under the column header you have inserted.

Reviewers will receive this Order Number in the Request for approval email and it will display in the Approval Form the reviewer will review. If you do not want this column to show in the Approval Form the reviewer will review add the pre-fix FW to the column header. Eg. Order Number will become FW Order Number. 

Decline the 1st form submission that was used to create a line on your spreadsheet.