Struggling with Custom Post type

It all seemed like a one two three thing. but i can't for the life of me get my custom post type to work.

im using the plugin 'custom post type ui'
i've created a cpt called: 'cb_chromebooks' . label plural is the same, label single is 'cb_chromebook'. I haven't touched any other settings in this cpt. i then went to tools and copied the code from 'all Custom Post Type UI posttypes' and pasted it into the functions.php

i have an ACF group called cb_chromebook_acfgroup. in this group i've added the rule: post type > equals > cb_chromebook ( as this singular form was what i could select from the drop down ).

i've then followed the instructions here: https://docs.generatepress.com/article/setting-up-a-simple-custom-post-type/ ( updated may5th ) meaning i did the following:

	<li>copied 'single.php' and renamed the new file to 'cb_chromebooks.php'</li>
	<li>copied 'content-single.php' and renamed the copy: 'content-cb_chromebooks.php'</li>

in the original files: single.php and content-single.php i added an echo telling me what file was used on the frontend to show the content. i added: Echo "current file single.php"; just before the comment: 'generate_after_primary_content_area_hook'

i did the same for the other 3 files, (added an echo there so i knew what was being loaded.)

i then opened the 'cb_chromebooks.php' file and changed the following:

`<li>old line: 'generate_do_template_part( 'single' );'</li>
<li>new line: 'get_template_part( 'content', 'cb_chromebooks' );'</li>`

i manually created a post from the new custom post type, can be found here: https://www.chromeo.nl/cb_chromebooks/test-cb_chromebooks/

On the frontend it shows that it used 'content-single.php'. What am i missing? because i'm stuck not being able to use the php that i need to create the content.

i have created a temporary user for support to use if need be.