Grafana + InfluxDB: Bad Gateway

I’ve been ecountering a weird issue with Grafana when trying to set up InfluxDB: even though the config for the data source is correct, when trying to test it it returns InfluxDB Error: Bad Gateway.

The problem is a really silly one. The default URL is http://localhost:8086. I tried manually inputting this, but it returned the same error.

The correct way of configuring this is http://localhost:8086/. Appending the extra / to the end fixed the problem, and Grafana can now connect to the data source.