Welcome to the PayPal Community! I'm sorry to hear you've run into some issues with a recent invoice you've sent. I would recommend double-checking it was sent to the right email address. If it was, they should see it in their PayPal Activity to be paid. It should say "Pending" on both yours and their side until the buyer initiates the payment. Just in case you need it, here's a great article on Invoicing with PayPal.
Good luck with this and future transactions,
- Jon K
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