The company file version is not supported

Just checking, but yourCompany_FIle_URI should have a UID at the end:
https://arl2.api.myob.com/accountright/<UID>

And have you created the token using the username and password?

Yes I am using Company_File_URI/Company_File_ID

Yes I have created the token.

OK, I thought that might be the case but just checking.

I have had this issue once before, and that was when I created a new MYOB business using the website instead of using the AccountRight desktop software. Using the website (I am not sure exactly where I was because MYOB has so many different domains that I get lost) it must have created a type of Company File that was unable to be accessed using this particular API. IIRC I was able to make some of the initial requests but then got denied with the same error message you are getting when trying to go further.

Once I installed the actual AccountRight software in a virtual machine, and created a business there, I was able to use the API and complete my integration.

This might not be your issue, but do check your account type to make sure it is a compatible MYOB product, which are alluded to here:
https://developer.myob.com/api/myob-business-api/api-overview/getting-started/