How can I run two separate journeys (e.g., a re-engagement journey and a scheduled promotional journey) at the same time without sending messages from both to the same user?

You can keep two journeys from messaging the same user at the same time. The simplest option is global frequency capping; if you need precise, per-journey control, use a tag plus a Condition split.

Option 1 — Global frequency capping (simplest)

Set account- or app-level caps so a user cannot receive more than N messages in a given period, regardless of which journey sends them. See Global frequency capping. This does not let you choose which journey wins, so use option 2 when the re-engagement flow must take priority.

Option 2 — Mutual exclusion with a tag

Create a Boolean tag in advance, for example in_winback_flow.

Re-engagement journey

1. Entry: use an Audience-based entry on an inactivity segment (for example, Last Application Open more than 3 days ago).
2. Mark the user: right after the entry, add an Update user profile element and set in_winback_flow to true. (This element replaced the old "Set Tags" element; it can set up to 10 tags at once, manually or from event attributes.)
3. Send your re-engagement messages.
4. Detect re-engagement: add a Wait for Trigger element on the activity event you care about (for example PW_ApplicationOpen).
5. Clear the mark: after the trigger fires, add another Update user profile element that sets in_winback_flow back to false.
6. Exit: finish that branch with the Exit from journey element.

To measure re-engagement (rather than control the flow), define the activity event as a Conversion goal instead: click Settings on the journey canvas and select Conversion goals. Conversion goals are a journey-wide setting, not a canvas element, so they do not create a "Goal Reached" branch. In the same Settings panel you can also configure Cancel events, which remove users from the journey without counting a conversion.

Promotional journey

1. Entry: your main audience.
2. Before each message element, insert a Condition split.
3. In the split, choose Tag as the condition type, select in_winback_flow, and add a branch for the value true. Leave that branch empty (or route it past the message) so those users skip the send.
4. The automatically created All other users branch goes to your message element, so only users not in the win-back flow receive it.

A Condition split can branch on a Segment, a Tag, or an Event attribute, and supports up to 10 branches.

Result: inactive users are tagged and shielded from promotional sends; as soon as they come back the tag is cleared, they exit the win-back flow, and they become eligible for the next promotional message.