Could be a type error for example. You specify an `int` column(say you expect "20") in the fdw but one row has it as `text`(you get "twenty"). Something like t

Could be a type error for example. You specify an `int` column(say you expect "20") in the fdw but one row has it as `text`(you get "twenty"). Something like this has happened to me when reading from a csv file. In this case pg will show an error and not read any rows from the fdw.