Can I mark an invoice as open (sent) when I print and mail as some clients don’t have email?

The Open (Sent) status will only apply on emailed invoices, aalinton.

You can send the invoice to your email. Just add a memo saying your client doesn't have an email address to avoid confusion.

I'm sure your clients have mobile phones. You can actually share the link (URL) of their invoices via text or using any messenger apps. Then, all they need to do is open the link using a mobile browser to see their invoice. You may want to introduce that option to them. You can also try it yourself.

Comment below when you want to know if a certain feature is available. You can also use the Help option in the upper right-hand corner to search for the feature you like.