The company file version is not supported
I am connecting to the MYOB API using Postman and am able to authenticate and List company files and API info. I can also query a single file by Company_File_URI and Company_FIle_Id to successfully ...
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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/
