Have you tried adding an InfluxDB API token (shown in the ‘provisioning’ bit of that guide)?
If you’ve setup influxdb within HA rather than following Sandy’s install guide linked from there, it might need some additional authorisation and presumably an API token is how it likes to do it!
The API token only appears to be generated via the cloud installation. For all intents and purposes mine should be very similar to the one in the tutorial.
Probably some silly user error on my side.
I’ll take a look at MQTT and see if I can get my head around that - might be simpler.