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Postsiva validates text length before posting. Over-limit text returns HTTP 422 with the platform name and character count.

Primary limits (captions / post text)

Secondary limits (titles / descriptions)

Multi-platform posting

When posting to multiple platforms, each platform is validated independently. A caption valid for LinkedIn (3,000) may fail on Bluesky (300):
Returns 422 for Bluesky even if LinkedIn would succeed.
Use platform overrides to send different lengths per destination: threads.threads_text, instagram.instagram_text, etc.

Example: platform-specific text

For Bluesky, trim default_text to 300 chars or add a shorter override in a pre-processing step.

Error format

Per-page LinkedIn/Facebook maps show the key in the label:

Quick reference by use case

Platforms overview

All eight platforms

HTTP errors

422 validation errors