Trying to send an Invoice and the SEND button is greyed out.

Hello, Barbara.

Let's run some troubleshooting steps so you'll be able to send your invoices in QuickBooks Online.

You might have experienced some browser-related issues that's why you're unable to send the invoice. Sometimes too much cache stored on a browser can cause unexpected behavior on the software. Let's fix it by accessing your account using an incognito window. This mode helps since this doesn't save any site data. Here are the shortcut keys:

• Google Chrome: press Ctrl + Shift + N 
• Mozilla Firefox: press Ctrl + Shift + P
• Safari: press Command + Shift + N

If it works, return to your regular browser and clear the cache. Doing this helps improve the system performance and eliminate unwanted site data. Alternatively, you can use a different supported browser.

Additionally, I've included this article for future reference: Record invoice payments in QuickBooks Online.

Don't hesitate to click the Reply button if you need further assistance in sending invoices. It's always my pleasure to help you out again.