/precheck — is the offline scope allowed for this app? (no login)
/auth/login?v=0 — scope "trade account_manage payment offline_access"
/auth/login?v=1 — scope "trade account_manage payment offline_access openid"
/auth/login?v=2 — scope "trade account_manage payment offline_access openid email profile"
/auth/login?v=3 — scope "trade account_manage payment offline"
/auth/login?v=4 — scope "trade account_manage payment"
A scope the app is not allowed to request fails the whole login — check /precheck first and pick an ACCEPTED variant.
/refresh/again — refresh with the stored token (longevity test, run it days later)