OK, yes you will need to convert the data back from string to array format. Here is what I recommend:
Go to Pre-request Script tab of the Create Role request, and insert the following code:
// Get rolepermission data (currently stored as string)
var roles = pm.iterationData.get("rolepermission");
// Convert roles back to a JSON array
pm.globals.set("rolepermission_array", JSON.stringify(roles));
Then you should modify the Create Role body to use this new array variable:
{
"role": {
"name": "{{rolename}}",
"description": "{{roledescription}}",
"permissions": {{rolepermission_array}},
"userType": "{{roletype}}"
}
}
Now you should find that the structure of your permissions is correct