I can't help you with the ingredients of this particular brand you describe, but there is a possible solution to your problem.
My advice would be to buy the simplest and least expensive Mg supplement at the pharmacy and give it a try.
I recommended the Liver Flush to a friend and she couldn't drink Epsom Salt at all. In the end she did the flush with regular magnesium supplement. She took magnesium in the evening (10 tablets instead of the daily dose of 4 as written on the bottle, which amounted to about 1000 mg) 2 hours before oil and juice mix and did a salt water flush in the morning. It was a success, she had no problems and did get the green stones out, so she is willing to do it again.
I am still doing the flushes with Epsom Salt as my taste buds agree with it.