Do you know if there is a way to set Priority system field in automation depicted below and using JSON ?

I have tried to add the below JSON under Additional fields
{ "fields": { "Priority": { "name": "High" } } }
but it results
->
Unknown fields set during create, they may be unavailable for the project/type. Check your custom field configuration. Fields ignored - Priority (priority)
As the rule is about creating request, does Priority field be part of the Request Form?
Note the automation rule is defined under TEAMS not Global Automation!