Probably wasted some money but at least you know he is healthy.
The significant weight loss can be explain especially if the first wait was not on empty.
It not uncommon for them to fast during winter months/breeding season I have some doing so anywhere between 6 to 9 months.
If the husbandry is optimal, stress is minimal (limit your handling) all you can do is wait it out, he knows how to eat and will resume feeding when ready.
Meanwhile make sure he is well hydrated and keep monitoring him.
It happens, it's frustrating but you'll get used to it.