graphQL - metaobjectUpsert and metaobjectCreate, error 'Value is invalid JSON: unexpected token'

Technical Q&A

Topic summary

A developer encountered a persistent error when using Shopify’s GraphQL metaobjectCreate and metaobjectUpsert mutations: “Value is invalid JSON: unexpected token at ‘gid://shopify/TaxonomyValue/1’”.

The Problem:

  • Variables were formatted according to official Shopify documentation examples
  • The same format worked when querying existing metaobjects
  • Standard JSON encoding of the entire payload (used successfully for other mutations like productCreateMedia) failed
  • Particular confusion arose around color_taxonomy_reference field, which returns as an array but wouldn’t accept array input

The Solution:

  • Certain input variables require double JSON encoding: first encode the specific field values as JSON strings, then encode the entire payload again
  • This non-standard approach differs from other Shopify GraphQL mutations

Outcome:

  • Issue resolved with double encoding
  • Developer requests Shopify update documentation to explicitly note when double encoding is required, as this behavior is inconsistent across their API and cost significant debugging time
Summarized with AI on October 27. AI used: claude-sonnet-4-5-20250929.
1

Hi,

Have got an irritating issue with graphQL calls to either create or upsert metaobjects. They always give the same error: Value is invalid JSON: unexpected token at ‘gid://shopify/TaxonomyValue/1’.

Here’s the variables object I’m passing in:

dartacus_0-1750089345421.png
dartacus_0-1750089345421.png800×794 77.2 KB

…and that matches up pretty exactly to the example in https://shopify.dev/docs/api/admin-graphql/latest/mutations/metaobjectcreate

When I query this metaobject, the existing entries it returns are all in that format. For example here’s a dump of the ‘green’ entry, as it is returned from the metaobject API call:

[4] => stdClass Object
(
[node] => stdClass Object
(
[id] => gid://shopify/Metaobject/167683359049
[handle] => green-reference
[type] => shopify–color-pattern
[displayName] => Green reference
[fields] => Array
(
[0] => stdClass Object
(
[key] => label
[value] => Green reference
)

[1] => stdClass Object
(
[key] => color
[value] => #05AA3D
)

[2] => stdClass Object
(
[key] => image
[value] =>
)

[3] => stdClass Object
(
[key] => color_taxonomy_reference
[value] => [“gid://shopify/TaxonomyValue/9”]
)

[4] => stdClass Object
(
[key] => pattern_taxonomy_reference
[value] => gid://shopify/TaxonomyValue/2874
)

)

)

)

The sharper-eyed among you will have noted that color_taxonomy_reference is an array: I’ve tried providing that field as an array when I try to create one and it doesn’t work either.

Any ideas anyone?

(PS: respectfully, please don’t pitch your service or app to me, this is a technical question and I’m hoping for answers/suggestions, I am not looking to install anything or outsource anything, thank you)

Many thanks,

G

2

Thanks Samuel. I forgot to add that the query string and variables object are json-encoded before being POSTed. The same method works for other mutations that have a query string and a variables object that contain arrays, such as productCreateMedia, but I’ll try it anyway.

G

3

Well, I’m utterly amazed - that worked. Brilliant suggestion, thank you.

Completely strange and weird, though, to be honest. It’s just bonkers that certain input variables have to be encoded as json and then encoded as json AGAIN when creating the payload. I’ve never had to do this for any other API and I haven’t even had to do it for other graphQL calls that take arrays as inputs.

If any Shopify staff are reading this, please, please update your documentation to mention this when it’s required for a mutation. This cost me hours of time.

Thanks again Samuel.

G