"AWS::AppSync::Resolver" and " AWS::AppSync::FunctionConfiguration" gives invalid name error.

[Y2KForever]

I've been trying to deploy an AppSync API with SAM these last couple of days. Creating the actual API is no issue. However, whenever I try to create a resolver or a function I get an error that says: "Name contains an invalid character". Which I guess make somewhat sense for FunctionConfiguration since that actually have a property called "Name". However, resolver doesn't.

This is how the FunctionConfiguration looks like in my template:

BatchGetFunction:
    Type: AWS::AppSync::FunctionConfiguration
    Properties:
      Name: batchGetStreamerFunction
      ApiId: !GetAtt GraphQLApi.ApiId
      DataSourceName: !Ref StreamersDataSource
      FunctionVersion: 2018-05-29
      RequestMappingTemplate: !Sub |
        #set($keys = [])
        #foreach($id in $ctx.args.broadcaster_ids)
          #set($discard = $keys.add({
            "broadcaster_id": $util.dynamodb.toDynamoDBJson($id)
          }))
        #end
        {
          "version":  "2018-05-29",
          "operation":"BatchGetItem",
          "tables": {
            "${StreamerTableName}": {
              "keys": $util.toJson($keys)
            }
          }
        }
      ResponseMappingTemplate: !Sub |
        #set($items = $ctx.result.data.${StreamerTableName}.responses)
        $util.toJson($items)

And my Resolver:

UpdateStreamerResolver:
    Type: AWS::AppSync::Resolver
    Properties:
      ApiId: !GetAtt GraphQLApi.ApiId
      TypeName: Mutation
      FieldName: updateStreamer
      DataSourceName: !Ref StreamersDataSource
      RequestMappingTemplate: |
        {
          "version": "2017-02-28",
          "operation": "PutItem",
          "key": {
            "broadcaster_id": $util.dynamodb.toDynamoDBJson($ctx.args.broadcaster_id)
          },
          "attributeValues": {
            "broadcaster_name": $util.dynamodb.toDynamoDBJson($ctx.args.broadcaster_name),
            "category":          $util.dynamodb.toDynamoDBJson($ctx.args.category),
            "title":             $util.dynamodb.toDynamoDBJson($ctx.args.title),
            "isLive":            $util.dynamodb.toDynamoDBJson($ctx.args.isLive),
            "updated":           $util.dynamodb.toDynamoDBJson($util.time.nowISO8601())
          }
        }
      ResponseMappingTemplate: |
        $util.toJson($ctx.result)

Does anybody see a distinct issue with this template? I've looked for hidden unicodes but can't find any.