How to solve “SQL aggregate function not allowed”?

I want to get the cases per million where a table contains “Province Population” and another table “Interim” contains a column that has unique Epid_ID values. I want to divide the count of these “Epid_ID” values with the population where the data type of population is big numeric and I am using Big Query. Following is the sql query I have written.

 SELECT
Admin_Level_1_province,
count(Epid_ID) as cumulative_numbers,
(count(Epid_ID)/ppopn.Population) as case_per_million
FROM `interim-data.casedata.Interim` as Inte join `interim-data.casedata.Province Population` 
as ppopn
ON Inte.Admin_Level_1_province = ppopn.Province
GROUP BY Admin_Level_1_province , case_per_million 

The error I am getting is “Column case_per_million contains an aggregation function, which is not allowed in GROUP BY at [7:35]”

Following is my sample data for Interim:

 Admin_Level_1_province  Week_number  YEAR  Epid_ID
 Province 1                 21        2020  COV-NEP-PR5-RUP-20-00022
 Province 2                 21        2021  COV-NEP-PR5-RUP-20-00023

Following is my sample data for Province Population Table

  Province     Population
 Province 1    23456778
 Province 2    12345566

Answer

Try below instead

SELECT Admin_Level_1_province,
  count(Epid_ID) as cumulative_numbers,
  1000000 * (count(Epid_ID)/any_value(ppopn.Population)) as case_per_million
FROM `interim-data.casedata.Interim` as Inte 
join `interim-data.casedata.Province_Population` as ppopn
ON Inte.Admin_Level_1_province = ppopn.Province
GROUP BY Admin_Level_1_province