You dosed way to much.
The result of black tar could have been a couple of things.
Generally brain, CNS, Bone, are all targets for tiny doses for 3 or 4 weeks.
To get what could have been a reaction, is very uncommon, Generally it takes 5 days to start working.
Now Praziquantel that can be in a Moxidectin plus tube can cause a kill, typically associated with flatworms.
Praziquantel can be powerful on first dose, but PZQ typically works at much higher levels, on larval stage worms that are sensitive to calcium killing. The tiny holes of Praziquantel can cause outright killing.
Severe systemic infections are the best target of Praziquantel.
MOXI is more like a precision designer med, Praziquantel is more like a sledgehammer.
There are a few that have told me they had a reaction and kill at the higher level doses, but a small test dose is always advised, to prevent an adverse reaction, or risk of an adverse reaction.
Going to Black right away is unusual, but not outside of the range of reported reactions to MOXI Plus.
Normally people find the no reaction dose is 60 to 80ucg/kg/D. Many have done a month at this level and get into some very hard killing situations, especially when combined with 5mg/kg/D FenBen.
Total preparation to handle the toxins of a kill is required, and a lot of knowledge about how to keep your body face side up, when the killing gets bad.
Killing hard with these meds need precautions, and a body chemistry configured to take the load of toxins and demands this kind of situation entails.
Even with preparation, many find it gets scary real fast, so a support plan with someone that has gone through it is a good idea.