Hello @Kevin Mayfield 

%GetNext retrieves values from the JSON object/array and assigns them to a local variable. However, the BLOB/streams exceed the maximum local length (3641144), MAXLEN doesn't cause the issue because it's a registered object, and the values are currently stored in memory. Therefore, AFAIK FromJSON is not suitable for handling such a large dataset.

Hello @Jan K

Yes, PS256 is not supported.  Can you try it in python JWT library packages.

Hello @Ali Chaib

1. You need to create you're custom DTL under "HS.Local.FHIR.DTL"  
2. Once DTL is created. Execute set status = ##class(HS.FHIR.DTL.Util.API.ExecDefinition).SetCustomDTLPackage("HS.Local.FHIR.DTL")  this and this will configure the customize DTL entry in the  ^HS.XF.Config global it's responsible for execute your DTL
3. Here is the documentation which covers most customization.
4. As I mentioned earlier, You need to the additional properties in respective SDA extension class.