Hi,

The error you are seeing occurs when you try to access an attribute of a collection of objects (in this case rec.line_ids) as if it were a single object.

To fix this error, you need to iterate over the line_ids collection and set the debit and credit attributes for each object in the collection.

Here's an example of how you could modify your code to do this:

def action_adjust_amount_currency(self):
    for rec in self:
        if rec.manual_currency_rate_active==True:
            for line in rec.line_ids:
                line.debit = line.debit * rec.manual_currency_rate
                line.credit = line.credit * rec.manual_currency_rate
        else:
            return False

Regards