Hello, I'm trying to create a custom field in the POS tickets of version 16 of Odoo, but it keeps saying undefined 

I have created this field and this function in the pos_order.py file (I don't know if it is the correct file)
 
total_impuestos_personalizado = fields.Float(compute='_impuestos_personalizados') 

def _compute_custom_taxes(self): 
 for order in self: 
​taxes = order.fiscal_position_id.map_tax(order.taxes_ids) 
​result_1 = order.total_amount / (1 + taxes.amount) 
​order.total_tax_custom = order.total_amount - result_1 

and I have put these lines of code in the OrderReceipt.js file 

Inside the configuration 
this._addCustomFields(this._receiptEnv);

 Below the setup

 _addCustomFields(envreceipt) { receiptSend.receipt.total_tax_custom = receiptSend.order.total_tax_custom; }