Hello Niyas,
i did this in python:

def _prepare_invoice(self):
for rec in self:
res = super(saleorder, rec)._prepare_invoice()
res['sales_type'] = rec.sales_type
return res
and then added the field in report like this:

<div t-if="o.sales_type">
<strong>Sales Type:</strong>
<t t-esc="o.sales_type"/>
</div>

but iam getting this error message as below:

Error when render the template
AttributeError: 'account.move' object has no attribute 'sales_type'
Template: account.report_invoice_document
Path: /t/t/div[2]/div[2]/div[5]
Node: <div t-if="o.sales_type"/>

any idea

Seems you haven't added a field named sales_type in the invoice model, can you add the field and try the same again and see

Thank You it works now