GA4 Custom Dimensions flowing into GA, but can't run reports on it

Question

To facilitate A/B testing, I pass google analytics a custom dimension that tells GA whether this user has seen the A or the B experience. Then I run reports where I can see how the A users and B users engaged differently with my website. I've been doing this for years with Universal Analytics, but I'm having trouble getting it working in GA4. I think I have everything set up correctly, but when I run a report in GA4, it gives me no data for my custom dimension.

I pass the custom dimension to Google Tag Manager via the data layer. And Google Tag Manager is set up to send the dimension to GA4 on page load. In GA4, I registered the custom dimension as a user level dimension. When I go into GA4's debugger, everything looks great. The custom dimension shows up with the proper value set. However, I can't seem to run reports on this data.

I'm doing a super simple freeform exploration. For rows, I have my ab testing dimension. For columns, I just have active users (screen shot of all of this below). I would expect to see two rows that show the number of A users and number of B users. Instead I get one row that says "not set". Any ideas what the problem is? Thanks!

Answer 1

Can not tell when you set the custom dimension in GA4. Where you set it?

Maybe you set it as event parameter but from your GA4 setting. You need to specify it is a User Property in Google Tag Manager

Two potential place you set the custom dimension.

So I add screenshots in both place