UI/UX: Project-level custom field fails successfully

[Holmus]

How are you running Flagsmith

• Self Hosted with Docker
• Self Hosted with Kubernetes
• SaaS at flagsmith.com
• Some other way (add details in description below)

Describe the bug

When a user with Project Administrator role (only - no organisation admin) creates a custom field via Project Settings → Custom Fields, the save flow partially fails. The MetadataField is created, but the call that binds it to a content type returns 403, and the error is surfaced as a generic "Failed to save custom field" toast. The field is left orphaned in the project: it shows up in the Project Fields list but is bound to no entity, so it cannot be set on Features, Segments or Environments.

Steps To Reproduce

1. Set up a user with Project Administrator role only on a project, granted via a role linked to a group (no org-level admin).
2. Sign in as that user, open the project, go to Project Settings → Custom Fields.
3. Click Create Custom Field. Set name = example, type = int, entity = feature, toggle "Required" on.
4. Click Create Custom Field.

Expected behavior

The save completes successfully (preferred - project admins are the intended audience for project-scoped custom fields), or
The save is rejected cleanly upfront with a clear permission error, and no MetadataField is created.

Screenshots

Screen.Recording.2026-05-05.at.13.54.07.mov