BD-5520: Clarify Shopify custom external ID endpoint setup

[bre-fitzgerald]

Why are you making this change? (required)

Your reason here...

Related PRs, issues, or features (optional)

• BD-5520

Feature release date (optional)

• N/A

Contributor checklist

• I confirm that my PR meets the following:
  • I signed the Contribution License Agreement (CLA).
  • My style and voice follow the Braze Style Guide.
  • My content contains correct spelling and grammar.
  • All links are working correctly.
  • If I renamed or moved a file or directory, I set up URL redirects for each file.
  • If I updated or replaced an image, I did not remove the original image file from the repository. (For more information, see Updating an image).
  • If my PR is related to a paid SKU, third party, SMS, AI, or privacy, I have received written approval from Braze Legal.

Submitting for review

If your PR meets the above requirements, select Ready for review, then add a reviewer:

• Non-Braze contributors: Tag @braze-inc/docs-team in a comment below.
• Braze employees: Have any relevant subject matter experts (like engineers or product managers) review your work first, then add the tech writer assigned to your specific vertical. If you're not sure which tech writer to add, you can add braze-inc/docs-team instead.

Thanks for contributing! We look forward to reading your work.

[Copilot]

Pull request overview

This PR clarifies the documentation for setting up custom external ID endpoints in Shopify integrations. The changes improve the technical accuracy and readability of endpoint specifications, including better descriptions of required parameters, validation requirements, and failure handling behavior.

Key changes:

• Enhanced parameter table with required/optional indicators and data types
• Added detailed failure behavior and retry logic documentation
• Improved validation requirements and security considerations

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
_docs/_partners/ecommerce/shopify/shopify_standard_integration.md	Updated Step 4.2 to clarify endpoint specifications, parameter requirements, response expectations, and failure handling for external ID retrieval in standard integration
_docs/_partners/ecommerce/shopify/shopify_custom_integration.md	Updated Step 6.2 with identical improvements to endpoint documentation for custom integration flow

[bre-fitzgerald]

Hey @dkim32, just following up on this PR—lmk if this looks good to you!