Need to add purchase details against the sales invoice for Example against particular sales invoice we need to update that from which supplier we hv taken this material

I'm here to share some insights about adding purchase details against the sales invoice in QuickBooks Online (QBO), @tio2impex.

For the time being, you'll have to either add a custom field or utilize the Message on invoice or Message on statement section to record purchase details against your sales invoice. Please see the screenshot below for your reference.

To add a custom field, here's how:

1. Go to the Gear icon. 
2. Select All lists.
3. Click the Add custom field or Add field option.
4. Enter the custom field's name.
5. Under the Select form type section, click the All Sales forms box and enable the Print on form button.
6. Select Save. 

Also, to further guide you in personalising and adding specific info to your sales forms, I'd recommend checking out this article: Customise invoices, estimates, and cash memos in QuickBooks Online.

Please let me know if you have other concerns about managing sales invoices and income transactions in QBO. You can drop a comment below, and I'll gladly help. Take care, and I wish you continued success, @tio2impex.