Using telegraf MQTT to bring Shelly Plus H&T into influxdb

Sorry to mislead you, the final plugin won’t work for this.
See @ThiefMaster’s example.
If you don’t need nanosecond time precision, you can reduce your timestamp precision so that your points fall into the same series. Then, you can use Telegraf to merge them or you can write them to InfluxDB and let the database merge them.