plan_not_eligible

API access itself is never the reason. The REST API, the MCP server and webhooks are available on every plan — Free, Solo, Advanced, Business, Enterprise and every grandfathered tier — so authentication, /v1/workspaces/me and every capability whose feature your plan has always answer normally.

A single capability can be plan-locked while the rest of the surface works, because the product feature behind it is. The error names the missing feature: update_global_tone_of_voice, for example, needs companyToneOfVoice (Business and above). MCP keeps such a tool listed and returns this error when it is called, because hosts cache the tool list for the whole session — see MCP tools §2. Upgrading is the only fix; the per-capability locks follow the same plan matrix as the dashboard.

A workspace an agency pays for carries the agency's plan. The check resolves the plan the way the dashboard does: the customer that pays for the workspace first (an agency's Business subscription, for a client workspace it manages), the workspace's own customer record second. So a member of an agency-managed client workspace who connects from that workspace gets the same features the dashboard shows them.

To recover:

1. Open the dashboard and visit Settings → Billing.
2. Upgrade to a plan that includes the named feature.
3. Retry the request — propagation is immediate after the upgrade webhook lands (within a few seconds in normal operation).

The check reads the plan recorded on the workspace's customer record, which Scripe's billing webhooks keep up to date — it never consults the Stripe subscription's live status. A subscription in Stripe's dunning (past_due) keeps its plan until Stripe cancels it. If the workspace is on a plan that includes the feature and you still see this code, the record has not caught up with the upgrade yet; wait a few seconds and retry, and contact support if it persists.