To medicate for intestinal problems without a fecal analysis could make things worse if you treat against the wrong pathogen. Also, don't even know yet if frog is sick to blame condition on seller. They could have sent you a visually healthy and thriving frog and the trip stress give the upper hand to an opportunistic bug.
Repta Boost is a powdered nutrient for non-eating or very malnourished reptiles/amphibians. A Pedialyte (or similar baby unflavored electrolyte formula) bath is mixed at 1:10 ratio with 80F dechlorinated for 20 minutes or until cool; and it's objective is to hydrate, energize and provide a short term boost to help frog perk up and eat by itself. Good luck with fecal

!