Hi Sputy,

You do like:

# first get partneron sale order

partner = self.partner_id

# loop to check any product in sale line is exist in partner form or not if, then raise warning

for line in self.order_line:

    for product_tmpl in partner.PRODUCT_TEMPLATE_MANY2MANY_FIELD:

        if product_tmpl.id == line.product_id.product_tmp_id.id:

            # Here you can set warning whatever you want

* PRODUCT_TEMPLATE_MANY2MANY_FIELD (many2many field that you have taken in partner form)

Accept and upvote answer if helpful

Thanks and regards

Haresh Kansara