down payment (product.template) unit of measure (uom_id) error

The problem is that a new product of "Down payment" will be created automatically. During the creation, uom field is not able to set. 

the solutions for this issue are:

1/. make sure the Unit(s) UOM is exist. If not, you need to create one. 

2/. setup "User-defined Defaults", uom_id --> product_template in "field" and input "1" in json field. UOM id 1 is supposed to be Unit(s). If not, input the corresponding id of Unit(s).

 another option can be:

1/. Go to view form "view_sale_advance_payment_inv"

2/. invisible set to "0" for below field.

<field name="product_id" context="{'search_default_services': 1, 'default_type': 'service', 'default_invoice_policy': 'order'}" class="oe_inline" invisible="1"/>

3/. when you choose down payment, you will see a product field and you can create the "Down Payment" product from there.