@cohen.avraham, the json-api-options of the daml.yaml file contains options which the Daml Assistant (daml start) will pass to the HTTP JSON API binary (http-json-binary). You can see what those options can be by placing --help in that section like this:
json-api-options:
- --help
When you run daml start with --help in the json-api-options as above it will not complete, but show you the command line options for the Sandbox’s HTTP JSON API service. You will not see sandbox-port or json-api-port in that list. Consequently, if you try to include those two options in the json-api-options section of the daml.yaml file, you get “Error: Unknown option.”
The two options sandbox-port and json-api-port are command line options for daml start. The following will work:
daml start --sandbox-port 6865 --json-api-port 7575
See this related post, which explains that because the daml assistant has an --json-api-port option, you cannot put --http-port in the json-api-options section of the daml.yaml file. 