To tie your custom dimension ab_page_image into Shopify, you would need to modify the Google Analytics tracking script on your Shopify website. This modified script should send the ab_page_image value to Google Analytics whenever a relevant event occurs. The changes would need to be put in the Shopify system either in the form of Liquid code in your Shopify theme, or through additional JavaScript code based on where you’re collecting the ab_page_image values from. For instance, if ab_page_image is a metafield associated with a product, you would retrieve it using Shopify’s Liquid templating language and pass this value into the GA4 event being sent. A developer familiar with both Shopify and GA4 should be able to help set this up for you.