Under Class Declaration, the syntax for declaring metadata specifiers is statet as
UCLASS([specifier, specifier, ...], [meta(key=value, key=value, ...)])
where it actually is (for 4.20 at least)
UCLASS([specifier, specifier, ...], [meta**=**(key=value, key, ...)])
I’d also suggest to have the second key value without value asignment, because there are valid specifiers that don’t have values.