Try running these curl commands:
First run this one to generate a new access token for the user
curl https://api.particle.io/oauth/token -u your_oauth_client_id:your_oauth_secret -d grant_type=password -d username=joe@example.com -d password=examplepassword
Then run this one (with the access token generated above in place of the “1234”)
curl https://api.particle.io/v1/devices\?access_token\=1234
Does running these commands give you a device list?