What causes "Invalid source '{$this->source}' for '{$this->fieldName}'." in octobercms/october?

Verify a blueprint with that exact handle/UUID exists in an active theme (or as a plugin/content blueprint).

octobercms/october · error · SystemException

Invalid source '{$this->source}' for '{$this->fieldName}'.

Error message

Invalid source '{$this->source}' for '{$this->fieldName}'.

What it means

After confirming a source is set, getSourceBlueprint() asks BlueprintIndexer::hasSection($source) to resolve it to a section UUID; a falsey result means no known blueprint matches, and a SystemException naming the field is thrown. Unlike the compile-time verifier check, this happens at runtime against the indexer's registry.

Source

Thrown at modules/tailor/contentfields/EntriesField.php:357

    /**
     * getSourceBlueprint validates and converts source to a blueprint
     */
    protected function getSourceBlueprint()
    {
        if ($this->sourceCache !== null) {
            return $this->sourceCache;
        }

        if (!$this->source) {
            throw new SystemException("Missing source for '{$this->fieldName}'.");
        }

        $indexer = BlueprintIndexer::instance();

        $uuid = $indexer->hasSection($this->source);
        if (!$uuid) {
            throw new SystemException("Invalid source '{$this->source}' for '{$this->fieldName}'.");
        }

        return $this->sourceCache = BlueprintIndexer::instance()->findSection($uuid);
    }

    /**
     * getSourceFieldset returns the source fieldset definition for checking inverse relations
     */
    protected function getSourceFieldset()
    {
        if ($this->fieldsetCache !== null) {
            return $this->fieldsetCache;
        }

        return $this->fieldsetCache = BlueprintIndexer::instance()->findContentFieldset($this->getSourceBlueprint()->uuid);
    }
}

View on GitHub (pinned to b608633a7e)

Solutions

Verify a blueprint with that exact handle/UUID exists in an active theme (or as a plugin/content blueprint).
Rebuild the Tailor index: run `php artisan tailor:refresh` (or clear the application cache) and retry.
Fix typos so the source matches the blueprint handle exactly (path-style, case-sensitive).

Example fix

# before
fields:
  posts:
    type: entries
    source: blog/post

# after (matching existing blueprint handle)
fields:
  posts:
    type: entries
    source: blog/posts

Defensive patterns

Strategy: validation

Validate before calling

if (!\Tailor\Classes\BlueprintIndexer::instance()->hasSection($source)) {
    throw new InvalidArgumentException("Source '{$source}' not found in blueprint index — run tailor:refresh or create the blueprint.");
}

Type guard

function isIndexedSource(string $source): bool
{
    return (bool) \Tailor\Classes\BlueprintIndexer::instance()->hasSection($source);
}

Try / catch

try {
    // record operations using the entries field
} catch (\SystemException $e) {
    // source unresolvable: verify blueprint exists, run php artisan tailor:refresh, retry
}

Prevention

Run `php artisan tailor:refresh` after adding or renaming blueprints, before using fields that reference them.
Include tailor:refresh in deploy scripts so indexes are always current.
Prefer blueprint handles over UUIDs in sources to make drift visible in review.

When it happens

Trigger: `source: blog/posts` where no section blueprint with that handle or UUID is indexed — the target blueprint was deleted or never created, the handle is typo'd, or the index is stale because the blueprint was added after the last registry rebuild.

Common situations: Creating a new target blueprint but never running `php artisan tailor:refresh`/cache clear; renaming source blueprints; deploying to an environment where the referenced blueprint file is missing from the theme.

Related errors

AI-assisted analysis of octobercms/october@b608633a7e (2026-08-21). Data as JSON: /api/errors/c217241d412786b3. Report an issue: GitHub.