How do I allow tips on invoices I send?

[treehstn]

I have had people send me paypal invoices that had a box to add a tip.  I can't figure out how to put this on my invoices... and I haven't found any reference to it in the help documents.  Anyone know how to do this?  Thank you!

[sharpiemarker]

@treehstn 

Fill in the invoice fully and the tips option will appear on the right side column. It won’t appear if invoice is blank.