I appreciate you for following up on this thread, ralphrabbat.

As soon as the default attachment for W9 is available, I'll be sure to drop back into the thread and give you an update. This way, you can utilize the feature in your QuickBooks Online snappily. 

As of the moment, I'd recommend doing the workarounds shared on this thread if you didn't try it yet. 

I can see how default attachments in the invoice are essential for your business and others. With this, I'll route you to a page where you can post feature suggestions. This way, our engineers can discover a method on how to make this feature happen quickly. 

Here's how: 

1. Go to the Gear icon, then choose Feedback. 
2. Type your concern in the box. 
3. Click Next. 

Your valuable feedback goes to our Product Development team to help improve your experience in QuickBooks. Also, I'd advise checking our QuickBooks Blog page regularly to know our latest news and enhancement in QuickBooks.

Additionally, feel easy to run any customer reports to track all the transactions and personal information you've entered into the system. Then customize it to show specific details. For complete steps, visit this article: Run reports in QuickBooks Online.

Lastly, check out this page about managing your customer statements, payments, sales forms, refunds, credits, and other related matters: Sales and customers.

I'm willing to listen if you have other concerns about the features or handling customer invoices. I'm here whenever you need more help. Keep safe.