So basically, the problem is that resize_image cannot find your image because it’s not getting the full path.
The solution (that doesn’t involve manually writing in the full path into the shortcode) is to do something like this in the shorcode:
{% set document = page | default(value=section) -%} {# this ensures the shortcode works in both pages and sections -#}
{% set image1 = resize_image(path=document.colocated_path ~ receivedurl, height=250, format="webp") -%}
Essentially, page.colocated_path or section.colocated_path contain the path to where the colocated assets are for the page you’re currently processing, and you need to prepend the receivedurl with that path.