In Glo Invoice, tap New Estimate, pick the customer, add line items, and tap Send. You'll get a unique approval link the customer can open without logging in.
Customers can approve or decline each line item, sign with their finger, and you'll get an instant notification. Approved estimates can be converted to invoices in a single tap.
Sending by SMS gets the fastest response — text-first communication is built into the app for exactly this reason.