It is not supported by plumber. I think we decided it could lead to unfortunate behaviour, since the coma is a reserved character. I might be able to find the pull request detailing why we abandonned the idea.
If you check the openapi.json definition, it specifies hat the letters parameter is exploded:
{
"servers": [
{
"url": ""
}
],
"openapi": "3.0.3",
"info": {
"description": "API Description",
"title": "API Title",
"version": "1.0.0"
},
"paths": {
"/letters": {
"get": {
"summary": "Sort letters",
"description": "",
"responses": {
"200": {
"description": "OK",
"content": {
"application/json": {
"schema": {
"type": "object"
}
}
}
},
"500": {
"description": "Internal Server Error",
"content": {
"application/json": {
"schema": {
"type": "string"
}
}
}
},
"default": {
"description": "Default response.",
"content": {
"application/json": {
"schema": {
"type": "object"
}
}
}
}
},
"parameters": [
{
"name": "letters",
"in": "query",
"required": true,
"schema": {
"type": "array",
"items": {
"type": "string"
}
},
"style": "form",
"explode": true
}
]
}
}
}
}