A Meta Graph API token that can publish to your Instagram Business account.
Instagram's posting API isn't the account you log into — it's Meta's Graph API, and it only works with Business or Creator accounts connected to a Facebook Page. You'll convert your Instagram to Business, link it to a Page, create a Meta App, then exchange a short-lived token for a long-lived one that lasts 60 days.
Meta's Graph API only publishes to Business or Creator accounts. Personal Instagrams are invisible to the API — and the conversion is free, reversible, and doesn't touch your content or followers.
In the Instagram app: Settings → Account type and tools → Switch to professional account. Pick Business or Creator. Business unlocks a few extra endpoints (insights, messaging); Creator is enough if you only need to post.
Next: request instagram_basic + instagram_content_publish scopes, generate a User Token in the Graph API Explorer, exchange it for a Page Token, then exchange that Page Token for a 60-day long-lived one via /oauth/access_token. About 8 more clicks.