Take a look at the syntax of this. This is not written according to the Restful API documentation.
{"to": "bts4ydgrs",
"data": [{"340": {"value": {"fileName": "{{a.json.fileName}}",
"data": "{{a.json.data}}"
}}}],
"fieldsToReturn": []}}}
]}
"fieldsToReturn": []}"
If we strip down the Restful API to its core these are the key components. Click Request Body tab here for reference: https://developer.quickbase.com/operation/upsert
{ "to": "dbid",
"data": [{ "fid": { "value": "This is my text" }} ],
"fieldsToReturn": [ n... ] }
What you have above looks like there is duplicate text. I think you want something more like this but would need to test.
{"to": "bts4ydgrs",
"data": [{"340": {"value": {"fileName": "{{a.json.fileName}}",
"fieldsToReturn": [340]}"
