Search Impression share as calculated field

Hi all,

I’m encountering an issue while trying to calculate Search Impression Share in Looker Studio for grouped data (grouped by campaign names).

The formula I’m using is:
Search Impression Share = (Total Impressions / Total Eligible Impressions) * 100.

However, I’m unable to locate a field labeled “Total Eligible Impressions” in Looker Studio. I attempted to use a cross-calculated field, but that resulted in an error too.

Is there a specific way to retrieve “Total Eligible Impressions,” or a workaround to calculate this for grouped data? If anyone has faced a similar issue or has insights, I’d appreciate your help! This is the error i see with the cross-calculated field.

Thanks in advance!