curle_unsupported_protocol
Easy Fix
cURL · libcurl & CLI
libcurl code CURLE_UNSUPPORTED_PROTOCOL indicates unsupported protocol during libcurl option/runtime call sequencing.
Quick Answer
Error code CURLE_UNSUPPORTED_PROTOCOL on your cURL libcurl & CLI means: libcurl code CURLE_UNSUPPORTED_PROTOCOL indicates unsupported protocol during libcurl option/runtime call sequencing.. This is usually fixable — see the step-by-step guide below.
Affected Models
Likely Causes
How to Fix It
1
Capture verbose output (-v / --trace) and isolate the exact phase where CURLE_UNSUPPORTED_PROTOCOL appears.
2
Reproduce unsupported_protocol with a minimal request against a known-good endpoint.
3
Validate protocol, TLS, DNS, proxy, and timeout options tied to libcurl option/runtime call sequencing.
4
Adjust one option at a time until CURLE_UNSUPPORTED_PROTOCOL clears and transfer completes successfully.
5
Lock the fix into scripts/clients and monitor for CURLE_UNSUPPORTED_PROTOCOL regression.
Pro Tip
This is a common issue that most users can resolve without specialized tools. Try the first step before moving on to more complex solutions.
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