https://community.cisco.com/t5/devnet-sandbox/when-attempting-to-launch-sandbox-400-bad-request/m-p/5364899#M12109 <P>Hello, first time attempting to do this and I am using Firefox on Win 11 on a last gen PC.&nbsp;<BR /><BR />When I hit the launch Sandbox button in the DevNet I am getting the error:</P><CENTER><H1>400 Bad Request</H1></CENTER><CENTER>Request Header Or Cookie Too Large</CENTER> Sat, 24 Jan 2026 08:24:12 GMT justinsellstrucks 2026-01-24T08:24:12Z https://community.cisco.com/t5/devnet-sandbox/when-attempting-to-launch-sandbox-400-bad-request/m-p/5364899#M12109 <P>Hello, first time attempting to do this and I am using Firefox on Win 11 on a last gen PC.&nbsp;<BR /><BR />When I hit the launch Sandbox button in the DevNet I am getting the error:</P><CENTER><H1>400 Bad Request</H1></CENTER><CENTER>Request Header Or Cookie Too Large</CENTER> Sat, 24 Jan 2026 08:24:12 GMT https://community.cisco.com/t5/devnet-sandbox/when-attempting-to-launch-sandbox-400-bad-request/m-p/5364899#M12109 justinsellstrucks 2026-01-24T08:24:12Z https://community.cisco.com/t5/devnet-sandbox/when-attempting-to-launch-sandbox-400-bad-request/m-p/5364902#M12110 <P>I'm sorry, this was a browser issue. If there's a way to remove this post, let me know and I will.</P> Sat, 24 Jan 2026 08:42:29 GMT https://community.cisco.com/t5/devnet-sandbox/when-attempting-to-launch-sandbox-400-bad-request/m-p/5364902#M12110 justinsellstrucks 2026-01-24T08:42:29Z