How to make carpet shampoo?

Can someone post the "recipe " or link on how to make your own liquid shampoo for the carpet . I had to do a spot last night in one of the bedrooms when my teenage son broke his lava lamp (those are nasty btw) and realized that I need to do the rest of his room and probably the other rooms too. Out of carpet shampoo for the cleaner and vaguely remember someone posting a "clean diy" version instead of expensive store bought stuff . Thanks in advance !
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