Substack Publication posts API

Please help me write a data collection script with the EveryInfra Substack Publication posts endpoint (substack/publication_posts).

Endpoint contract:
- Request: POST https://api.everyinfra.com/api/v1/social with the header Authorization: Bearer <API key>. Read the key from the EVERYINFRA_API_KEY environment variable and never hard-code it.
- In the request body, set platform to substack and action to publication_posts, and put the parameters inside params.
- Required parameters:
  - url: Specifies the target Substack resource link. Use publication homepages for publication and publication_posts, or direct /p/ post links for post and comments.
- Optional parameters:
  - content_type: Filters publication posts by content format using all_types, newsletter_posts_only, podcast_episodes_only, or threads_only. (allowed: all_types / newsletter_posts_only / podcast_episodes_only / threads_only)
  - since: Specifies the start date string for filtering posts or activity feeds within a date range. Its presence in shared profile or publication parameters does not enable account creation date filtering.
  - until: Specifies the end date string for filtering posts or activity feeds alongside since. This parameter does not represent subscription expiration dates or trigger complete historical archive exports.
  - limit: The most rows to return in this call, an integer from 1 to 30. The default applies when you leave it out, and a call can return fewer rows. Larger values return 422 before any charge. (default: 10)
- Returns a list of records. Main fields of each record: id, url, title, subtitle, text, author_name, author_username, publication_name, publication_handle, publication_url, like_count, comment_count; 23 fields in total, full list at https://api.everyinfra.com/api/v1/social/catalog?platform=substack.
- Example request body:
{
  "platform": "substack",
  "action": "publication_posts",
  "params": {
    "url": "https://astralcodexten.substack.com"
  }
}
- Price: $1.39 per 1,000 requests; failed and empty results are not charged.
- For dozens or hundreds of targets, add "mode": "async" to the body: you get a job_id at once and poll GET https://api.everyinfra.com/api/v1/jobs/{job_id} for the result.
- On 422, fix the request using the suggested parameter names and allowed values in the error; on 429 or 503, wait for Retry-After and try again.

Before writing code, ask me which targets I need, how many, which fields, and what output format I want; then confirm the plan and the rough cost with me.