Am I doing something wrong?
Not necessarily The number of ads available can vary by region. The number of 150 credits is simply a ceiling and not a guarantee that there are videos available. Even when we could watch unlimited ads that was true.
As Callaghan159 suggests, you might want to try resetting your AD ID. If you're unfamiliar with that process, here's a link that explains the process (information also copied and pasted below):
- Go to Settings
- Scroll down to Privacy
- Scroll down to the bottom of the page and tap Advertising
- Be sure that Limit Ad Tracking is set to Off
- Tap Reset Advertising Identifier
- When prompted, tap Reset Advertising Identifier.
- Step 1: Open Google Settings on your Android device by tapping on menu and then on Google Settings once all apps are displayed on the screen.
- Step 2: Locate and tap on the Ads menu under Services.
- Step 3: Tap on "reset advertising ID" on the new page.
- Step 4: Confirm the reset when the confirmation prompt is displayed.