Problem: You may encounter dependency or compatibility errors if custom or third-party modules designed for older Odoo versions are used in Odoo 18.

Solution:
Review each custom module for any deprecated functions or changes in dependencies.

Update the modules' manifest.py file to specify Odoo 18 as the required version.
Test modules individually in a development environment to identify compatibility issues before deploying to production.

# In the __manifest__.py file, specify the Odoo version and dependencies
{
    'name': 'Custom Module',
    'version': '1.0',
    'depends': ['base', 'sale'],  # Add compatible dependencies
    'application': True,
    'installable': True,
    'auto_install': False,
    'license': 'LGPL-3',
    'version': '18.0.1',
}

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