Module development and code questions

I am trying to import views from one of my Drupal 9 sites, we will call it Drupal A to another Drupal 9 site, we will call it Drupal B. 

I keep getting this error: 

"Error message

The configuration cannot be imported because it failed validation for the following reasons:

I followed the  REST tutorial and then the instructions on how to make POST available ("create" option) but it does not work. The POST route is not recognized.

Version: 10.1.3

REST-UI: 1.21

Folder structure:

When creating a PHPUnit functional test on this route `/support_ticket/add/ticket` the "AssertionError: assert(!str_starts_with($data_type, 'entity:')" error occurs. I can't seem to find any information about what it means. When testing the same route in a browser a http 200 response is returned and the page renders correctly.

The questions I am searching information for are mentioned below. Any direction would be gratefully received.

I'm maintaining a new contributed module, Bootstrap Theme Toggler, and am having a problem with it failing a PHPUnit functional test that I've defined and included in the project.

Hello,

I want to run an ajax form, which is loaded itself (only the HTML) via ajax in jQuery

I load a form into a page in a boostrap modal using the following code called on Ajax (with a custom route) :

I maintain the amazon_pa module and now tried to upgrade to D10.

The problem is that the comoser repository uses guzzle 6.2 and that will throw the following error.