Unable to add dataset in the calculated field

Dataset name: Fact Flat PG
I am trying to link site with the dataset. I am unable to link the dataset in the calculated filed. Its give me error while I save.

Calculated field is:

ifelse(
${WeeklyFirstAttribute}=‘site’,{pg_group[Fact Flat PG]},
NULL)

Note: I was also doing the same kind of calculation with a with dataset fact_flat_unified . It was working.

Is it the name used as Alias, which is the reason its not working. Please give a check on the attached screenshots. You help will be grateful.

Hello, can you please share the error details. Or, upload the screenshot again.