If you create an expense where you were not the sole participant, but also paid for colleagues or externals, then it is useful to tag these in the expense so that your company knows who participated. 

Via Web Application:

You can do this by entering them in the comment field with the "@" sign. When you enter the "@", a drop down menu will appear:

You can simply select from your colleagues, or if you want to add a person from outside your company, you can click on "Add new guest" and enter the name, company and email (optional) to add him to your guests who will be stored in the list for the future:

After saving the changes to the expense you can see that the attendees were added successfully when their names are highlighted in blue:

Error message "The mentioned user's full name is not valid":

If after adding your attendee, you get a pop-up message saying "The mentioned user's full name is not valid", please check if there is a white space after the attendee's name and delete it.

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