In Pipedrive, a deal can only have one linked contact person at a time. However, if a deal has more than one contact person related to ongoing processes, you can add these additional people as participants.
To add participants, go to the Participants section of a deal detail view and click the “+ Participant.”
That will open a window where you can search for an existing contact person to add as a participant, or create a new person to add.
The new participant will appear in the Participants section of the detail view sidebar, and you can click “View All” to see a list view of the participants linked to that deal.
You can also click the gear icon in that window to customize the displayed fields.