I am looking for a voice leading error or chord construction error in this example but can’t seem to find one. Any pointers would be great!
The error is a so-called "hidden fifth", or, "direct fifth". Your outer voices are moving into a perfect consonance by similar motion. Even in strict voice-leading this is often allowed except in cases like this where the soprano voice leaps, rather than steps, into the consonance. This sheet is a pretty good guide for voice-leading if you're in a theory class, but keep in mind that strict voice-leading presupposes a specific set of goals. Exercises like this are great practice, but when you're actually writing music you get to set your goals for yourself, and that's half the fun of it! :—)