Insert auto number from main form into subform rows

Insert auto number from main form into subform rows

Hello.

I'm trying to take from my main form "order number" which i have setup as an auto generated number into every line created in my subform.

So when a row is created in my subform i want the "order number " from the main form to be inserted automatically.

struggling to work this one out.

any help appreciated.

Main form = 'order entry'
Sub form = 'order items'

the field has same name in both forms = 'order_number'