updatePost Mutation returning 500 server errors, but no error message.

Hi there!
I'm trying to update a post via API, and am running into some issues and would love an extra set of eyes.

I can update my post via UI just fine 👍🏼

If I copy the input variables from dev tools that made that mutation, and paste them into the Bettermode GQL playground, and get a 500 error returned without much else info.

Here's my mutation with identifying info removed in the playground

mutation {
  updatePost(
  id: "123",
  input: {
    locked: false,
    attachmentIds: [],
    slug: "abc-123",
    customSeoDetail: {
      thumbnailId: null,
      noIndex: null,
      description: null,
      title: null,
      canonicalUrl: null
    },
    mappingFields: [
      {
        key: "title",
        value: "I LIKE PIZZA",
        type: text
      },
    # some other fields here but all I want to update right now is title
    ],
    tagNames: [],
    ownerId: "hello world",
    publish: true
  }){
    createdAt
  }
}

Here's the error message returned

Is anyone able to help me get this mutation working? Thank you in advance!