I doesn't sound like you made the master page text box a Primary Text Frame. If it were, it would automatically generate a page after the first one.
Here's how they work:
https://indesignsecrets.com/indesign-basics-primary-text-frames.php
I believe that if you uncheck Limit to Primary Text Frames, you can get it to autoflow without Primary Frames, but only after you have created a new frame on a second page, linked to the frame on the first page as described in this article:
https://indesignsecrets.com/make-indesign-add-pages-automatically-as-you-type.php
"You can make Smart Text Reflow work on any text frame by turning off the limitation checkbox in the Preferences dialog box. However, in that case, you still won’t get it on every frame… it will only work for stories that are in frames that are already threaded across two or more pages! In other words, it won’t apply to any frame or story that is only on a single page. "