JSON API: Cannot connect to API when URL contains encoded slash


When creating a data source with the JSON API plugin for Grafana, I get an error message: “JSON API: Cannot connect to API”. But only for URLs that have a encoded slash, e.g. https://streamr.network/api/v1/streams/0x688759bcbb6adf32a07e91f6de84d181b252e655%2Fethereum-gas-prices/data/partitions/0/last

I can request the URL in a browser without errors.

Any idea? Should I encode/escape any character more?
Thank you.