I agree with spelling out the `address` field.
As for "value is either an address or an array of addresses", there is no standard for specifying an array in a URI, and processing different querystring schemes is application-specific. (see
https://stackoverflow.com/a/9547490)
Since those app-specific methods don't necessarily preserve order, which is important here, the most compatible fallback is a delimiter-separated list under one parameter. Most languages have library functions for splitting strings on commas.