Facebook launched instant games towards the end of 2017, most months after that they've brought in updates after updates making the life of a typical instant game developer pure pain.
Usually these changes revolved around code and business side of the game. Now it has gotten to a point these changes are affecting the development workflow.
Facebook decided to not show ads on instant games when played desktop unless the game has a minimum DAU (Daily Active Users).
Now, In order to test an ad, a developer actually has to create a Bundle and upload it to Facebook. Then use a mobile phone to test if the ads work. The limitations placed will not allows developer to properly debug an app. Solutions like v-console (an open-source project) are used by developers to view a developer console in mobile.
This is really annoying for developers who now cannot even easily test their ads implementation. The Facebook team confirms it will continue to use this design. Facebook Instant game team has always been non-responsive towards app developers' requests and this now makes a developer even more frustrated.