@Aaron Kiander Thanks for reaching out. From your description I understand that your attempt to use $submit operation by POSTing a PAS request bundle is failing.
I have checked this internally with our product team, and they confirmed that the $submit operation defined by implementation guide is not implemented on Api for FHIR yet. please feel free to leave your feedback at https://feedback.azure.com/d365community/forum/c2115f96-0625-ec11-b6e6-000d3a4f0858
Do let me know if you have any queries.
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