CURL FTPS failure (InitializeSecurityContext)

Using Curl 7.55.1 on Windows 10 attempting to confirm an FTPS server is using TLSv1.2. (If there's a better/easier way to do this, feel free to let me know)

I am running the command curl -v --insecure --tlsv1.2 ftps://[server:port] and receive the following response:

*   Trying [server]...
* TCP_NODELAY set
* Connected to [server] ([server]) port [port] (#0)
* schannel: SSL/TLS connection with [server] port [port] (step 1/3)
* schannel: checking server certificate revocation
* schannel: using IP address, SNI is not supported by OS.
* schannel: sending initial handshake data: sending 156 bytes...
* schannel: sent initial handshake data: sent 156 bytes
* schannel: SSL/TLS connection with [server] port [port] (step 2/3)
* schannel: encrypted data got 527
* schannel: encrypted data buffer: offset 527 length 4096
* schannel: next InitializeSecurityContext failed: SEC_E_INVALID_TOKEN (0x80090308) - The token supplied to the function is invalid
* Closing connection 0
* schannel: shutting down SSL/TLS connection with [server] port [port]
* schannel: clear security context handle
curl: (35) schannel: next InitializeSecurityContext failed: SEC_E_INVALID_TOKEN (0x80090308) - The token supplied to the function is invalid