## The symptom
PATCHing a merge field (e.g. `lists/{id}/merge-fields/{merge_id}` with
`options.choices`) via drewm/mailchimp-api failed with:
```
400 Invalid Resource: options.choices - Schema describes array, object found instead
```
The payload showed `{"options":{"choices":{"0":"Aaa","1":"Bbb"}}}`: the array
of choices had been encoded as a JSON object with numeric keys.
## Why
The wrapper passed `JSON_FORCE_OBJECT` to `json_encode`, which turns every PHP
array into a JSON object, breaking every API field that expects a real array.
## The fix
The maintainer merged a community PR fixing the encoding so non-associative
arrays serialize as JSON arrays. Upgrade drewm/mailchimp-api past the January
2016 fix.
## Same bug, other fields
The same encoding also explains failures on other array-expecting fields, e.g.
`recipients.segment_opts.conditions` on campaign creation. If you see "Schema
describes array, object found" anywhere with this wrapper, it is the same root
cause.