Holy moly, that is overpotted! Mine is two feet tall and thriving in a six-inch bulb pot. I water it once a month, when I remember.
Try putting it in Al's gritty mix in a smaller pot. Was it in the shade at Lowes ? If it was and you immediately placed it in the sun it would drop its leaves. Lighting changes must be gradual.
Don't give up, these guys are tough and will respond to proper care.

I agree with seedmoney they gritty mix would work best, mine trails over its pot. If you can't repot right away the soil should dry out before it should be watered

Agreed. Pot too big, bad soil. That little fella will be dead in no time with that combo, so as noted above, look up gritty mix, and get it into a smaller pot.

Joe

I would remove it from that pot to let it dry out for a few days. Repot into a fast draining mix and DO NOT water for another 5-7 days. Are you keeping the plant indoors or out? If out, where do you live? Your weather has a lot to do with how often you should be watering, especially now.

Nancy

Portulacaria afra can happily go 6-9 months without any water at all. It's drowning.

Since this post I have moved my plant into a clay pot and it's in gritty mix it's seems to be doing better now. I live in Washington state and keep it indoors in my bedroom window now. Since repotting I haven't watered it . It's slowly coming back to life.

Delighted to hear the good news!

GREAT! :)