In casual American English, when -en or -on follows certain consonants, the schwa vowel is dropped and N becomes syllabic [n̩] — it forms its own syllable without a vowel before it.
The small line under the N [n̩] indicates it's syllabic.
Syllabic N commonly occurs after:
See Glottal Stop + Syllabic N for more on the T + syllabic N pattern.