Not able to convert value field when writing to InfluxDB

I’m not familiar with using InfluxDB as a destination, but we have a user having trouble converting the value field in their pipeline. Anyone happen to know how he might be able to solve this?

“...it seems that the value field (the one I specify in the value fields input box) are all stored as String, even though I converted it to Double using a Field Type Converter before sending it to InfluxDB. Do you use the line protocol when writing to InfluxDB?”