Potential typo in the API doc and API Explorer and Developer Guide. Both say "resolution", but the little yellow box in API Explorer uses faxResolution, and that's the one I tried and it worked.
https://developer.ringcentral.com/api-explorer/latest/index.html#/!/Messages/post_v1_0_account_accou...
https://developer.ringcentral.com/api-docs/latest/index.html#!#RefCreateFaxMessage
https://developer.ringcentral.com/api-explorer/latest/index.html#/!/Messages/post_v1_0_account_accou...
https://developer.ringcentral.com/api-docs/latest/index.html#!#RefCreateFaxMessage
