I still don’t know if this is local to my tennant, but I have tried in 2 different orgs, and I always get an error with Customer field for Contact. This post is almost identical to the Set Parent Lookup, but there are some differences in the end.
Setup Contact
I have one Excel file with 6 contacts. They are linked to the account with number 311. The unique identifier I have on contact is email.

I setup a key for email on contact, so that the system will understand what to write to.

Setup Account
On the Account I have 2 fields for number matching, because I have different systems that integrate, but it doesn’t matter in this case. PO Account Number is what we are going to use, and I will try to explain why (based on my findings).

PS: Both Account Number and PO Account Number are Alternate Keys on Account!!
Setup Data Flow
Go to https://make.powerapps.com and start a new Data Flow project. In this case I am choosing the Excel file for simplicity. I have uploaded the Excel file to One Drive, so that it is available at all times online.




In the Excel file I had to make sure that the first row was headers before i continue

During the mapping I will see both the Alternate Keys I have for account. Normally you probably only have 1 Alternate Key for Account, but my setup requires 2 because of 2 different systems integrating against 2 different numbers. For blog i am using value 311, so it doesn’t really matter here.

When done mapping Account Number (again it doesn’t matter if I choose one of the other) continue to the next step. I choose a manual refresh, and it get stuck here.

You will also see an error in the data flow projects.

https://admin.powerplatform.microsoft.com
Open data integrations, and open the one that failed.

From here you can open the mapping table

This is where you most likely will see a missing mapping. For some reason it cancels out my mapping. I have tried this in 2 environments and same issues. Every time i choose the Customer Lookup i have this problem.

Click on the destination field, and navigate WAY to the bottom.

This is where I believe the bug is located. Data Flows happens to be sensitive to what Alternate Key was created last. This key is the last thing that I published on Account, and therefore it is in the list. If you only have 1 alternate key, this will show.
Again, it doesn’t matter in this demo because i have 311 in both KEY fields.

The Work Around
After you save the changes, open Data integration. Here you will setup a schedule to run from the admin.powerplatform.microsoft.com.


Click save schedule and wait for it to run.
PS!! Remember to stop the schedule when done!

For the Final result you will see 6 contacts connected to the Account

Next up is how long does it take to import 94000 contacts to CDS via Data Flow!