Challenge Not yet complete... here's what's wrong: 'Activate Temp Access Flow' lightning app page doesn't exist with the flow component called 'Accounts Temp Access'. Check the instructions.

Has anyone passed this challenge? I have passed all prior challenges. It seems pretty straightforward, I have my Lightning app page, activated it, added it to Sales...everything else is setup and has passed. 

Error: Field must be grouped or aggregated: et4ae5__Contact_ID__c. I need to return the Contact ID and the max DateOpened grouped by Contact. I don't think et4ae5__Contact_ID__c is a groupable field. This is in workbench SOQL query. Please help!

SELECT MAX(et4ae5__DateOpened__c),et4ae5__Contact_ID__c
FROM et4ae5__IndividualEmailResult__c
WHERE et4ae5__Opened__c=TRUE
GROUP BY et4ae5__Contact__c

This is the one I started with:

SELECT et4ae5__DateOpened__c,et4ae5__Contact_ID__c
FROM et4ae5__IndividualEmailResult__c
WHERE et4ae5__Opened__c=TRUE
ORDER BY et4ae5__DateOpened__c DESC
LIMIT 1
GROUP BY Contact_ID__c

I followed the instructions, make the previous challenges and now I can not pass this ... Has anyone completed it already?

P.S. An apology if my writing is not very good, my native language is Spanish

Error: Field must be grouped or aggregated: et4ae5__Contact_ID__c. I need to return the Contact ID and the max DateOpened grouped by Contact. I don't think et4ae5__Contact_ID__c is a groupable field. This is in workbench SOQL query. Please help!

SELECT MAX(et4ae5__DateOpened__c),et4ae5__Contact_ID__c
FROM et4ae5__IndividualEmailResult__c
WHERE et4ae5__Opened__c=TRUE
GROUP BY et4ae5__Contact__c

This is the one I started with:

SELECT et4ae5__DateOpened__c,et4ae5__Contact_ID__c
FROM et4ae5__IndividualEmailResult__c
WHERE et4ae5__Opened__c=TRUE
ORDER BY et4ae5__DateOpened__c DESC
LIMIT 1
GROUP BY Contact_ID__c

I am still learning about triggers and for some reason following is not working. Any idea what is wrong? I do not get an error message, just that the trigger does not update the custom field. 

trigger populateRecName on Account (after insert,after update) {
    
    for(Account acc: trigger.new){
        if(acc.RecordType.Name == 'Joint Account'){
            acc.rec_type__c = 'Joint Account';
            update acc;
        }
    }
   
}