Multi City is a feature where products will show on city based, You can create single/multiple city from admin panel and assign product to single/multiple city.
Add City: You can add single/multiple cities from admin panel goto MultiCity => Major Cities.
Add Location & Postcode: You can add single/multiple minor cities & postcode from Admin Panel goto MultiCity => Minor Cities.. Also check how to add bulk minor cities or post code here: https://myportalcode.com/account/knowledge_article/?ticketknowledge_section_id=2&ticketknowledge_article_id=10
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