I appreciate you for using QuickBooks Online as part of your business. I'm here to help you sort out this issue with sending your invoices.
Beforehand, I'd like to ask for additional details to help me get on the same page. Like, have you encountered error messages while doing the process? This way, I can check on my end if other users have the same error you encountered.
Since you're able to re-subscribe to QBO, we can try logging into your account using a private window. Thus, there are times when too much historical data from the browser causes discrepancies that affect the view and performance of your QuickBooks. As a result, you may be unable to send invoices.
To help us determine if this is a browser-related issue, feel free to use either of these keyboard shortcuts to open an incognito window depending on your browser: