Can't make listbox with multi select transfer to excel cell with comma's between selection

I'm really new to VBA and have been teaching myself over the last week. I'm trying to make this userform simple for the people that I work with as they are not computer literate but I am stuck on this listbox and making it transfer the selected items to the cell.

Any help is appreciated.

This is the code I have for the text box itself:

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and this is the code I'm trying to use on the command add button:

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