Currently either $this->parent_base returns the wrong (empty) base, or 'wp/v2/' is missing from the base.

Actual Location header

    c.a.w.w.v.Client.debugRequest() - Request Entity: <POST http://johan-wp/wp-json/wp/v2/posts/3766/meta,{key=Gomxw, value=bLfaU},{Authorization=[Basic am9oYW4ubXluaGFyZHQ6d29yZHByZXNzIQ==]}>
    c.a.w.w.v.Client.debugHeaders() - Response Headers:
    ...
    c.a.w.w.v.Client.lambda$debugHeaders$8() - Location -> [http://johan-wp/wp-json/posts/3766/meta/11965]
    ...

Expected Location header

    c.a.w.w.v.Client.debugRequest() - Request Entity: <POST http://johan-wp/wp-json/wp/v2/posts/3766/meta,{key=Gomxw, value=bLfaU},{Authorization=[Basic am9oYW4ubXluaGFyZHQ6d29yZHByZXNzIQ==]}>
    c.a.w.w.v.Client.debugHeaders() - Response Headers:
    ...
    c.a.w.w.v.Client.lambda$debugHeaders$8() - Location -> [http://johan-wp/wp-json/wp/v2/posts/3766/meta/11965]
    ...