Sometimes, you will need to add permission or assign multiple users using People Picker field. This post tells you how you can insert multiple user entities using COPY (CTRL + C) and PASTE (CTRL + V).
First of you, make sure your user logins are in claims format. The reason why you need it to be in this format is that the SharePoint People Picker cannot identify of which provider the login if it is not in the full format…
Refer to link here for all the format required.
Append “;” at the back of each login
i:0e.t|identity provider|[email protected];i:0#.w|domainA\domainuser1;
Additonal Note: SharePoint People Picker allows you to quick Check Name by hitting Ctrl + K