Unable to connect to WPGraphQL

I am new to building with Gatsby and wordpress. when i run "gatsby develop", i get this error on my command line
"Unable to connect to WPGraphQL, Either WPGraphQL is not active or there are some WordPress PHP filters in your site which are adding additional output to the GraphQL response. These may have been added via custom code or via a plugin". I have activated and reactivated the WPGraphQL(Version 1.19.0) plugin but it is still not working. please i need help in fixing this