Unexpected error posting mutation via graphql

Posting a mutation to standalone:v20.03.1 via /graphql endpoint that works with Altair results in a curious error:

panic: graphql op error:
{"query":"\nmutation AddPerson($person:AddPersonInput!) {\n\taddPerson(input: [$person])\n\t{\n\t  worker {\n\t\temail\n\t\tfirstName\n\t\tlastName\n\t  }\n\t}\n  }  \n","variables":{"person":{"email":"foo@bar.com","firstName":"Foo","lastName":"Bar"}}}
graphql error:
no query string supplied in request

I checked the source for that error, at /graphql/schema/request.go:40

	if req == nil || req.Query == "" {
		return nil, errors.New("no query string supplied in request")

and the test is for the json struct member query which clearly is in the payload. Problem with named operations?

Solved. The URL was malformed:


Note the duplicated forward slash after the port.