her eyelids twitch

To solve the problem of twitching eyelids we need to find out its cause first.
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There may be two of them:

1. The client is excited, perhaps, she drank a cup of coffee before the procedure or just constantly thinks about her problems.

Ideally, you should accustom your clients not to drink coffee before the extension, as it will distract you from work and your client won't be able to lie calmly for 2-3 hours. But if this has already happened, you need to relax the client. Turn on quiet music and cover her with a warm blanket, gently and calmly suggesting that she should sleep. Try to stop a possible conversation so it will be easier for the client to calm down (and for you to work).⠀

2. This is a natural feature of a human that even while sleeping the eyes keep moving, making the eyelids shiver.

Well, in this case, it is necessary to act more persistently. I mean to physically fix the eyelids in one position. Some trainers advise gluing a couple of upper lashes to a patch, but I personally don't approve such a method, since the client may feel discomfort because of this tension. And certainly, no coins ????Money is THE DIRTIEST thing in the world, literally. This is the main breeding ground for bacteria. You can't even imagine how many people touched this coin before you did!⠀
It's better to use a thin strip of microfoam tape. Gently stick one end of the strip to the eyelid, pull forward (ask the client if there is some discomfort) and then tape the second end to the skin. The easiest way is to pull the middle part of the eye, which is the last thing what lash techs usually work on.