Thumnail Image not working in Sub Domain

Hi All

Need some advise. I had migrated a site from the main domain to a sub domain and use the WP import plugin to move the post to the new sub domain.

However, the thumbnail images in the sub domain is not showing up. The theme is using Tim Thumb script (had upgraded to the latest version). Inside the post, image is showing up fine.

The image URL from the existing post is of course pointing to the main domain for example, https://mydomain.com/wp-content/uploads/20xx/0x/xxx while I understand that the new image would be stored in https://xx.mydomain.com/files/20xx/xx/xx

The TimThumb script is not generating the thumnails from it although it’s supposed to work in WP Multisite. Any idea on how to resolve it?

Thank you in advance.