The filter has correct syntax, but the fields not exist, you won't get any error.
If the syntax is incorrect, the flow will throw the error when you run it.
So, please double check on your side carefully.
You can use the URL to verify your filter.
For example, when you open Regional Sales Sample in PowerBI online,
in the address bar of your browser, remove experience=power-bi after question mark?
then add filter=Territories/Territory eq 'US-WEST'
if it give you the same result as without filter, then the field is not correct, you have to double check it.
You can go to the report, click .... (More options).
Then Choose 'Explorer this data (preview)'.
on the popup window, on the right panel, hove over your mouse on Territory field, it will give you the table/field data.
See below.