Categories and Tags not working for new posts on self-hosted sites (iOS app)

[debonid]

Description

Title

Categories and Tags not working for new posts on self-hosted sites (iOS app)

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Describe the bug

On self-hosted WordPress sites, categories and tags cannot be assigned to new posts in the iOS app. The issue affects both reading and writing taxonomy data depending on the device and post type.

Behavior

Feature	iPhone (26.9)	iPad (26.9)
Existing posts - Categories	✅	✅
Existing posts - Tags	❌	✅
New posts - Categories	❌	❌
New posts - Tags	❌	❌

When trying to add a category, the app returns:

"There was a problem communicating with the site. An HTTP error code 403 was returned"

Tags fail silently without any error message.

Steps to reproduce

1. Add a self-hosted WordPress site to the app
2. Create a new post
3. Try to assign a category or tag
4. Category list is empty, adding a new category returns 403 error
5. Tags can be typed but are not saved

Expected behavior

Categories and tags should load and be assignable on new posts, same as on existing posts.

Technical investigation

Extensive debugging was performed across multiple self-hosted WordPress sites:

• REST API endpoints /wp-json/wp/v2/categories and /wp-json/wp/v2/tags return correct data (Status 200) when tested directly in browser
• Application Password authentication works correctly when tested via browser console with Authorization: Basic header — returns Status 200 with full category data
• No server-side blocking confirmed — the issue occurs across multiple sites with different plugins and configurations
• Tested on multiple self-hosted sites on Hostpoint.ch (Switzerland) — all fail
• A self-hosted site on a different hosting provider (Hoststar) works correctly with the same app version
• Issue persists after:
  • Full app reinstall
  • Revoking and regenerating Application Passwords
  • iOS and app updates
  • Network reset on iPhone
  • Testing on both WiFi and mobile data

Environment

• WordPress app version: 26.9
• iOS version: 26.5
• Device: iPhone 15 Pro and iPad (both same iOS and app version)
• WordPress version: 7.0
• Hosting where issue occurs: Hostpoint.ch (Switzerland)
• Hosting where it works: Hoststar.ch (Switzerland)

Additional context

The same app version on iPad shows partial functionality (existing post tags work, new post tags do not). On iPhone the issue is more severe. Browser-based wp-admin works correctly on both devices. The issue appears to be hosting-provider specific rather than plugin or configuration related, as it affects all sites on Hostpoint regardless of their individual setups.

Step-by-step reproduction instructions

Steps to reproduce

1. Add a self-hosted WordPress site to the app
2. Create a new post
3. Try to assign a category or tag
4. Category list is empty, adding a new category returns 403 error
5. Tags can be typed but are not saved

Screenshots, screen recording, code snippet

No response

Environment info

No response

Please confirm that you have searched existing issues in the repo.

• Yes

[dangermattic]

Thanks for reporting! 👍