Query not working within [slug].js file in nextjs - using acf

I've recently set up a Next.js project along with a headless Wordpress CMS. My posts & pages are using custom Gutenberg blocks to pull content through. I've set up the following plugins on the CMS:

WP GraphQl, WP GraphQL Gutenberg, WPGraphQL for Advanced Custom Fields and ACF Pro.

Within ACF I have set up an 'Image' Block, which has a text field and an image field.

Within my code, I have a query in my lib/api.js file like below (14 is the ID for the current image selected - this will change):

export async function getImageById() {
    const data = await fetchAPI(
      `
      query GetImageDetails($id: Int = 14) {
        mediaItems(where: {id: $id}) {
          nodes {
            mediaItemUrl
            mediaItemId
          }
        }
      }
      `
    )

    return data;
}

My folder structure is as follows.

• lib
• components
  • Blocks
  • universalImage.js
• Pages
  • blog
    • index.js
    • [slug].js
• Public

If I call the query in my index.js file, it returns info on the media image:

export default function Home({posts, first, imgs}) { 
   console.log(imgs)

   return(
      <div>
         //all my content
      </div>
   )
}

export async function getStaticProps() {
    const images = await getImageById();
    const jsonI = await images;

    return {
        props: {
            imgs: jsonI
        }
    }
}

However if I try to call it in my [slug].js file I get back an empty array

[slug].js code

export default function Post(postData, imgs) {
   console.log(imgs)

   return(
      <div>
         //all my content
      </div>
   )
}

export async function getStaticPaths() {
  const allPosts = await getAllPostsWithSlug();

  return {
    paths: allPosts.edges.map(({node}) => `/blog/${node.slug}`) || [],
    fallback: true
  };
}

export async function getStaticProps({ params }) {
  const data = await getPost(params.slug);
  const imgs = await getImageById();

  return {
    props: {
      postData: data.post,
      imgs
    }
  }
}

I am new to Next.js and React so maybe I'm missing something obvious, however any help would be appreciated as I can't progress much further in the project.

Also if you need any more info please let me know.

FetchAPI function is:

async function fetchAPI(query, { variables } = {}) {
  // Set up some headers to tell the fetch call
  // that this is an application/json type
  const headers = { 'Content-Type': 'application/json' };

  // build out the fetch() call using the API_URL
  // environment variable pulled in at the start
  // Note the merging of the query and variables

  const res = await fetch(API_URL, {
    method: 'POST',
    headers,
    body: JSON.stringify({ query, variables })
  });

  // error handling work
  const json = await res.json();
  if (json.errors) {
    console.log(json.errors);
    console.log('error details', query, variables);
    throw new Error('Failed to fetch API');
  }
  return json.data;
}