I recently came across an error like this when looking through application logs at work:

Error: org.postgresql.util.PSQLException: ERROR: value too long for type character varying(3500)

It's an application that I'm not 100% familiar with yet and it wasn't clear which table and column the error message was referring to. All I knew was that it was some varchar(3500) column. Fortunately, PostgreSQL makes it easy to query the database schema.

FROM information_schema.columns
WHERE table_schema = 'public'
    AND data_type = 'character varying'
    AND character_maximum_length = 3500;

In my case it narrowed things down to a few possibilities of which one was the obvious answer. Hopefully you have the same luck.