Can I issue stock from QBO to project but not generate invoice? How to manage this transaction?

Yes, @phyllis-chng-efu, you can still issue stock for the project without generating an invoice in QuickBooks Online. Let me discuss the process of managing this transaction.

If your customer has paid on the spot, you can issue stock for the project by creating a sales receipt. However, if you intend to invoice them later, you can create an estimate so they know what they can expect to pay. 

To create a Sales Receipt:

1. Click + New, then Sales receipt.
2. Select the customer from the Customer dropdown. 
3. Enter the sales info, such as the Payment method.
4. From the Select a product/service ▼ dropdown, choose the stock items that you sold.
5. (Optional) You can edit your line item’s quantity or rate in the Qty and Rate field.
6. When you're done, select Save and send to email the receipt.

To create an Estimate:

1. Click + New, then Estimate.
2. Select Add customer. Then select a customer from the ▼ dropdown. 
3. Fill in the necessary fields.
4. When done, hit Save.

I'm adding these articles to learn more about tracking inventory items in your QuickBooks company: 

• Set up and track your inventory in QuickBooks Online   
• Use reports to see your sales and inventory status in QuickBooks Online

Let me know in the comments below if you have further questions about managing your stock items in QuickBooks, @phyllis-chng-efu. I'll be around to lend a hand.