Expected json but got plain text in Apollo Studio

I am trying to query from my router/subgraph and I am able to run it locally, but I keep getting this error while in Apollo Studio:

HTTP fetch failed from ‘oralbCombined’: HTTP fetch failed from ‘oralbCombined’: subgraph didn’t return JSON (expected content-type: application/json or content-type: application/graphql+json; found content-type: "text/plain")

I’m not sure what the problem here is or how to fix it. It see’s the subgraphs and everything in the query section, but it can’t return anything. Anyone have ideas?