Sounds like the vendor you're working with is a bit stuck in their ways, but I'm actually a fan of Paypal (and have been since before they merged with competing payment system X.com, eons ago!) and applaud them for requiring a paper trail for transactions.

Now it turns out that you can send a request for either side of the transaction, a request for payment, and an actual payment, but the advantage of the request for payment invoice is that the recipient cannot send the money to the wrong address: they simply respond to the payment request and it's all filled in automatically.

Fortunately, I recently found myself working with a company that asked me to send them a payment request so I captured all the steps.

Here's how it works:

Step zero, of course, is to go to the Paypal site and log in to your account.

Notice I'm not offering you a clickable link. Paypal is one of those sites when you should never, ever click on a link to visit. You should always just type in the URL in your browser to ensure that you don't get ensnared by a phishing attempt!

Along the top you'll see that there's a "Request Money" option:

Click on it and you'll see that there are a small number of fields to fill in:

(I have blurred out the recipients email addr and account name for privacy: hopefully on your screen the information will be readable!)

The most important thing here is to choose between Goods and Services. If it's not an explicit physical product, then choose "services". It sounds like the company requesting your Paypal payment request is a service company too.

Click on "Continue".

At this point Paypal should confirm that the email addr you entered as the recipient of the payment request has an account. Look for "Verified Business Member" and look for an account name - or user name - being expanded from the email addr. Make sure it matches up with what you expect!

It's always helpful to enter a note here too, even if it's just "as requested".

Click on "Request Money" and it's sent!

You'll also get an email confirmation that you requested a payment:

Note that the email confirmation is not the same as a notification that the payment was made. That's a different email, and as with any email you get from Paypal, it's always a good idea to go to the site (type in the URL, remember, don't click on a link in the email) and confirm that the money has indeed been received.

Good luck and I hope they pay promptly.