A purchase invoice generated from multiple Goods Received Notes is a useful feature that allows you to consolidate several documents into a single invoice. You can create such an invoice directly from the GRN list. To do this, go to
.

Select the GRNs you are interested in. Right-click on the selected row, then go to Generate... and choose Generate FVZ from the submenu to create a sales invoice.

These two documents will be automatically combined into one purchase invoice.

Use the button Links to check the links between documents.

You can also manually add additional items. Do this by clicking the Add button. Then select the desired product from the list and add it. A confirmation message will appear, which you should accept.

The document has been updated.

You can also manually link the invoice with other documents. Go to Links, then click Edit connections.
Select the document you wish to link to your purchase invoice.
At this point, you have three GRNs linked to one purchase invoice.