go to post Lori Fassman · Jun 4, 2017 More on this - turns out that Extension fields need to be enclosed in an <Extension> element, like so:<Allergy> <Extension> <Mode>SNAPSHOT</Mode> <OnsetDate>20170412113619</OnsetDate> <AllergyType>ALLERGY</AllergyType> <AllergyStatus>ACTIVE</AllergyStatus> <Asserter>10262187</Asserter> </Extension> <AllergyCategory> <Code>DA</Code> </AllergyCategory> <Allergy> <SDACodingStandard>DRUG</SDACodingStandard> <Code>d00116</Code> <Description>penicillin</Description> </Allergy> <Severity> <Code>SEVERE</Code> </Severity> <DiscoveryTime>2017-04-12T00:00:00Z</DiscoveryTime> <FromTime>2017-04-12T00:00:00Z</FromTime> <Status>A</Status> <EnteredAt> <Code>UHC</Code> </EnteredAt></Allergy>