I tested this on my test store a few times and wasn’t able to replicate the same results you are getting. It may be possible that the values you are using are off but I can’t be sure without seeing them for myself.
If you are a Shopify Partner, you can contact our Partner Support team by heading to the Support menu of the Partner Dashboard and connect with them directly. They can gather the necessary authenticated information that we require to investigate from there.
I’ve tried to replicate this error again on our test store and we are still unable to replicate, indicating the draftOrderCreate mutation is working as expected with a valid purchasingEntity input, including a CompanyID, CompanyContactID, and CompanyLocationID.
If you’ve confirmed that the id’s that you are including in the input are correct and existing entities on the store, please do reach out to our support team with specific examples of the query returning the error and we can help look into this further with you directly!
Here’s an example graphQL query you can run to check that you are using the correct ID’s in your draftOrderCreate mutation: