Dogs are much less sensitive to it than humans, according to the article.

A quick Google search leads to an FDA article for veterinarians that says “only a tiny amount” can cause an overdose though.

¯\_(ツ)_/¯

Unsure of the specific pharmacokinetics behind it but dogs take about 3x mcg per kg dosing compared to humans. A lethal dose of fentanyl for humans is 100-200 micrograms which would theoretically translate to about 600mcg lethal dosage for dogs. Considerably larger than a humans tolerance but still only a few granules of powder would be lethal

They sell there kibble and bits for the money to score.