1. Create an Action Button:

• Add a button in your custom module's view to trigger the creation of the invoice.

2. Define a Python Method:

• Define a Python method in your module that will be called when the button is clicked. This method should create the necessary logic for generating the invoice.

3. Create a Wizard/Dialog:

• Create a wizard or a popup dialog (similar to the one in the sale module) using Odoo's views and forms.
• Define the fields and layout for this wizard in XML.

4. Trigger the Wizard from the Button Click:

• In your Python method, when the button is clicked, open the created wizard or dialog using Odoo's action mechanism.

Example Steps:

Create Button in View xml:

Python : def open_invoice_wizard(self):
    # Logic to prepare data for the wizard if needed
    return {
        'name': 'Create Invoice Wizard',
        'type': 'ir.actions.act_window',
        'view_mode': 'form',
        'res_model': 'your.invoice.wizard.model',
        'view_id': self.env.ref('your_module.xml_id_of_wizard_view').id,
        'target': 'new',
        # Any other necessary context or default values
    }
Wizard View (XML): your.invoice.wizard.form your.invoice.wizard.model Wizard Model (Python): class YourInvoiceWizardModel(models.TransientModel):
    _name = 'your.invoice.wizard.model'

    # Define fields for the wizard

    def create_invoice(self):
        # Logic to create invoice based on the provided data in the wizard
        # This method should create the invoice using Odoo's API
        # Once the invoice is created, you can handle further actions if needed
        return {'type': 'ir.actions.act_window_close'}

Ensure to replace 'your_module', 'your.invoice.wizard.model', 'xml_id_of_wizard_view', and other placeholders with your actual module and view names.

This general approach allows you to create a custom button triggering a wizard or dialog for creating invoices in your custom module similar to the behavior in the sale module.