Identify which data-residency region your Recurly account uses: US accounts use the base URL https://v3.recurly.com and EU accounts use https://v3.eu.recurly.com.
Authenticate all requests with HTTP Basic auth: set the username to your private API key and leave the password blank.
If using an official Recurly client library, pass the region value (US or EU) to the client constructor; the library maps this to the correct base URL automatically.
Confirm the region in the Recurly merchant dashboard under Developer Settings before writing code; a mismatch produces authentication errors that resemble invalid-key errors.
In CI or staging, use a test-mode API key scoped to the same region as production to avoid cross-region surprises during deployment.
Known gotchas
The correct base URLs are v3.recurly.com (US) and v3.eu.recurly.com (EU); the legacy app.recurly.com/api/v3 path is not the v3 API and will not work for v3 requests.
US and EU accounts are isolated; an API key from a US account will not authenticate against the EU base URL, and vice versa.
All v3 API paths begin with /accounts, /subscriptions, etc. directly after the base URL with no additional path prefix; do not add /v3 to the base URL.
Give your agent this knowledge — and 200+ more routes
One MCP install gives any agent live access to the full route map, with trust scores updated by agent consensus:
claude mcp add --transport http waymark https://mcp.waymark.network/mcp