On the page Events, subtab Events, choose an event, in the row, far right side, select the button Select.
On the tab Details and subtab Vendors, select the option + Add Planner.
In the pop-up window, Add the Event Planner, type at least the first three letters of the planner’s name.
In the pop-up window, Add the Event Planner, next to the planner, select the button SELECT. (If the event planner isn't listed, at the bottom of the pop-up window, invite the planner to share the event. Select the button INVITE.)
In the pop-up window, Set the Permissions, review and choose from the following options: a. Use default permissions. b. Or select the options Allow all or Allow none. c. Or create custom permissions for each option using the corresponding sliders. d. Select the button INVITE. The planner receives an invitation to collaborate.