Why am I not able to associate tax in the bill for an unregistered vendor?

If the Vendor is unregistered under GST Preference, then tax can be associated on the basis of Reverse Charge.

First, we need to configure the tax preference of the organization by enabling reverse charge for Sales transactions. Here’s how:

• Go to Settings in the top-right corner.
• Click Taxes under Taxes & Compliance.
• Click GST Settings from the left menu.
• Mark the Enable Reverse Charge in Sales transactions checkbox under Reverse Charge.

Here’s how you can enable the reverse charge option and associate tax:

• Go to Purchases from the left sidebar and click Bills.
• Click +New under Bills.
• Select the This transaction is applicable for reverse charge checkbox and enter the required details.
• Click Save.