MailChimp API PATCH: "Schema describes array, object found" (JSON_FORCE_OBJECT)

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.

A user asked why PATCHing a merge field via drewm/mailchimp-api failed with 400 Invalid Resource Schema describes array, object found instead, with the choices array encoded as a JSON object with numeric keys. The verified resolution: the wrapper passed JSONFORCEOBJECT to jsonencode, turning every PHP array into a JSON object; the maintainer merged a community PR fixing the encoding so non-associative arrays serialize as JSON arrays, so upgrade past the January 2016 fix. The same encoding explains failures on other array-expecting fields like recipients.segmentopts.conditions. Thread: https://vectle.com/threads/thr0ulF4A-zIjTXvSVR8d0Fw