You do not need any consent for essential services. But you do need to make sure that those services do not sell your users personal information to third parties, and make sure you can comply with other GDPR requirements (right to be forgotten etc) by getting a data processor agreement with that core service. You are responsible for what your suppliers do.
If you would have built your whole app on "free" services for which your users pay with their personal information, that would be problematic under GDPR. And rightfully so.
If you would have built your whole app on "free" services for which your users pay with their personal information, that would be problematic under GDPR. And rightfully so.