Lack of AU (Assignable Unit) file

Been working with Articulate Storyline and have never had this issue so I'm hoping someone will be familiar with this and offer a solution.

Once we output the learning module for a product we usually launch it on our own LMS site. But sometimes, the different carriers for the product also wants the module to put on their site. We've never had issues distributing to carriers until recently. Only one carrier is saying the file doesn't have an AU and is affecting their ability to launch the course.

Per their own words: "It looks like there is no Assignable Unit (AU) or Lesson contained within the course. True SCORM format will use an AU or lesson to launch open. There should be a way within the storyline development tool that you can add an AU. "

Has anyone come across this issue before? I found two posts on this forum from Justin Grenier that mentioned Assignable Units. He mentioned:

In most Learning Management Systems, you don’t have to manually point to a specific file to launch content, as long as that content is compliant with SCORM, AICC, or xAPI. You simply upload a compliant zip file, and if the LMS is compliant with the same standard, it knows where to look to find the files that launch the content.

For example, the AICC Packaging Specification says that the .au file (at the root of the zip file) tells the LMS everything it needs to know about how to launch and track the content.

If you are using an AICC LMS that needs to be manually told where to find the assignable unit in a Rise course, it is located at ⁠⁠⁠scormdriver/indexAPI.html⁠⁠⁠, but I’m a little nervous that the LMS may not pick up everything it needs to know from that file.  Contrast this with testing your content at SCORM Cloud and you'll see how streamlined the process can be.

I can't find the .au file in the root directory like he is saying and i can't find the scormdriver/indexAPI.html file path he mentioned in his comments. Since both mentions were in a post from 3 and 4 years ago, respectively, is this something the articulate doesn't use any more or is it located somewhere different.

Hoping you guys can point me towards a solution. I'm at little bit at a loss. Files attached.

Added note: thank you everyone for your wonderful insights. It's been very helpful in guiding our client. I took the attachment files down to limit their exposure now that I feel like we have enough direction.