Sidekick: Add Checkout Address Validation

Help me add address validation to my Shopify checkout:

Store name: [YOUR STORE NAME]
Shipping countries: [LIST COUNTRIES YOU SHIP TO]
Current address error rate: [PERCENTAGE OF ORDERS WITH ADDRESS ISSUES]
Monthly order volume: [APPROXIMATE ORDERS PER MONTH]

Implement address validation at checkout:


  
    Address autocomplete - Add Google Places or a similar address autocomplete service to the checkout address fields. As the customer types their street address, show a dropdown of matching addresses. When selected, auto-populate the city, state, postal code, and country fields.
  
  
    Real-time validation - Validate the entered address against a postal database (USPS for US, Royal Mail for UK, etc.) before the customer proceeds to the next step. Check that the street address exists, the postal code matches the city and state, and the address format is correct.
  
  
    Suggestion prompts - If the entered address is close but not exact, show a suggestion: “Did you mean [CORRECTED ADDRESS]?” with options to accept the suggestion or keep the original entry. This catches common typos and abbreviation issues.
  
  
    Apartment and unit validation - If the address appears to be a multi-unit building but no apartment or unit number is provided, show a gentle prompt: “This address may require an apartment or unit number. Would you like to add one?”
  
  
    PO Box detection - If your shipping methods do not deliver to PO Boxes, detect PO Box addresses and show a message: “We cannot ship to PO Boxes. Please enter a street address.” Block checkout progression until a valid street address is provided.
  
  
    International formatting - Support address formats for each country you ship to. Automatically adjust field labels and order based on the selected country. For example, show “Postcode” for UK addresses and “ZIP Code” for US addresses.
  
  
    Saved addresses - For returning customers, allow them to select from previously validated addresses stored in their account. Pre-fill the form with their default address.
  
  
    Error reduction metrics - After implementation, track the reduction in failed deliveries, returned packages, and customer support tickets related to address issues.
  


Recommend the best address validation app or API integration for Shopify.