Can we get a CURL test for POST to /TOKEN?

We have a third party (mobile app) testing against the exposed iMIS REST API.

They are sending this CURL:
curl -H "content-type: application/x-www-form-urlencoded" -d '{"grant_type":"password","username":"XXXXXXX","password":"XXXXX}' -v 'https://ourclientdomainiscorrect/Asi.Scheduler_USAB/Token'

They receive this error:
{"error":"unsupported_grant_type"}

Does anyone see a problem with the CURL or could we get a proper CURL to send over to them that assuredly is good to receive the TOKEN?

A lot of people use CURL to test. Asking them to switch to Postman is a non-starter.

Jack Donahue