I’m having this exact same error, calling out position 3 which is the colon after 301. I’ve tried saving as .yaml and uploading but it gives the same error. I’ve also run the code through https://jsonlint.com/ and it dings that colon with the following message:
Invalid JSON!
Error: Parse error on line 1:
301: /benefits-sessio
—^
Expecting ‘EOF’, ‘}’, ‘,’, ‘]’, got ‘:’
On Windows, depending on your settings, the extension might not be displayed. When you save, do save AS, and make sure to choose the ‘all files’ format, removing the .json extension. (I suspect you saved it as filename.yaml.json …)