X_CLIENT_SPEC_UNSUPPORTED
Means
x client met an OpenAPI construct its compiler refuses
Typical cause
the source document uses a construct the compiler does not read (the cause names its JSON pointer): not, if/then/else, patternProperties, a non-JSON body, a cookie parameter
Fix
x help client --json — then rerun with --only naming the tags around the pointer the cause names, or pin a corrected source.json