Why is BigQuery Sandbox saying its ERROR: Expected keyword AS but got "(" at [1:17]

Question

Is this an issue with BigQuerry. I was follwing along with this youtube video and for some reason this code will not work.

    WITH pop_vs_vac (continent, location, DATE, population, new_vaccinations, rolling_people_vaccinated)
AS (
    SELECT dea.continent, dea.location, dea.DATE, dea.population, vac.new_vaccinations, SUM(CASt(vac.new_vaccinations AS INT)) OVER (
            PARTITION BY dea.location ORDER BY dea.location, dea.DATE
            ) AS rolling_peoploe_vaccinated --(rollling_people_vaccinated/population)* 100
    FROM [gg-analytics-404715.Portfolio_Covid.Covid_Deaths] AS dea
    JOIN [gg-analytics-404715.Portfolio_Covid.Covid_vaccinations] AS vac
        ON dea.location = vac.location
            AND dea.DATE = vac.DATE
    WHERE dea.continent IS NOT NULL
        --- order by 1, 2, 3
    )
SELECT *
FROM pop_vs_vac