TLS 1.3 not supported

When configuring HTTPS as documented here :
https://tyk.io/docs/basic-config-and-security/security/tls-and-ssl/

Choosing TLS1.2 “min_version”: 771 works.

Choosing TLS1.3 “min_version”: 772 fails with this in gateway log

http: TLS handshake error from 192.168.63.227:54194: tls: client offered only unsupported versions: [303 302 301]

I am assuming you are using the packages from packagecloud. Those are built with go 1.12 which requires an environment variable

GODEBUG=tls13=1

See https://golang.org/doc/go1.12#tls_1_3 for more details.