I can't use the Gemini 3.5 Flash model in the AI Studio App Builder (agent) workspace. Is anyone else facing this same problem?

If anyone has a solution to this problem, please share it. Before, it was telling me my credits had run out even though I hadn’t used it at all. Now, it starts running for a few seconds and then says ‘An internal error occurred’ every single time. I submitted feedback, but they still haven’t solved the issue.