Paid plans (403 plan_feature_unavailable), up to 3 links on Starter, 5 on Basic, 10 on Pro and 25 on Agency (422 link_limit_reached). alias is Pro and Agency only (403 alias_requires_pro) and unique in any letter case (409 alias_taken). Refused with 422 destination_not_allowed (details.reason says which check): links to other shorteners, mulaichat.com itself or private networks, online gambling, domains on the Komdigi block list, and destinations Google Web Risk suspects of phishing or malware. The same checks run on a new destination and every day on active links, which are blocked when one fails. Requires the write scope.