I complete an invoice and preview to send but when I check back in the status page is says overdue but Not sent, I go back to the invoice and still says preview and send

I know the reason why the completed invoice still shows overdue in QuickBooks Online, @robertsonagricul.

Some email providers are blocking invoices that are successfully sent out from QBO. 

Our community is already aware of this issue and is currently trying some steps to address this. Rest assured, we're keeping an eye on it and this is a top priority for us. 

In the meantime, I recommend following these options as an alternative to sending invoices;

• Save the invoice as a PDF and send it via email through the company or another email address.
• You can use SMS or messenger service to send your customer a link to their invoice. Simply select "copy link" from the "save and share link" menu and paste it into your SMS or IM service.
• You can send invoices from your own address if you have a Gmail or G-suite email account:https://quickbooks.intuit.com/learn-support/en-us/help-article/invoicing/use-gmail-address-send-invoices/L7bMJtO01_US_en_US?uid=l3xdrgw2 
• You can save the invoice as a PDF, print and mail it to your customer.

I'm also adding this helpful guide you can review about handling sales forms in QBO: Customise invoices, estimates, and sales receipts in QuickBooks Online.

You can always reply to this thread if you need extra help with invoices or QuickBooks. I'm always willing to assist. Stay safe.