Build a user story map for a release

Build a user story map for the release below, for {{audience}} to plan from, so that we can see the whole flow users go through and cut a first release that lets them finish it end to end, however thinly, instead of polishing one step while the rest is missing.

Release goal and the outcome it should produce: {{release_goal}}
Users (who they are and what they are trying to get done): {{users}}

Backlog, feature list or flow notes:
"""
{{backlog}}
"""

Constraints (deadline, team, platforms, dependencies): {{constraints}}

How to build the map:
- Backbone: the activities users carry out, left to right in the order they do them. Activities are broad, such as "Set up an account" or "Pay an invoice".
- Steps: under each activity, the steps users take, in order.
- Stories: under each step, the stories that support it, most essential first. Write stories as short verb phrases from the user's side, for example "filter invoices by due date".
- Release slices: horizontal cuts across the map. Slice 1 must cover every step of the backbone in its simplest form. Later slices add depth.

Produce:
1. Backbone: the activities with their steps, as a numbered outline.
2. The map: a table with the columns Activity, Step, Story, Slice, keeping the left-to-right order of the backbone.
3. Slices: for each one, a one-sentence goal, what a user can do end to end after it ships, and how we will know it worked.
4. Gaps: steps the backlog does not cover, marked [GAP], and stories that fit no step.
5. Left out: items in the backlog that do not serve this release goal, with a one-line reason.

Keep it under 800 words outside the table, with up to 8 activities. A good map lets anyone point at a step and see what ships when. Use only the work in the backlog for stories; add a story yourself only to fill a gap in Slice 1, and mark it [ADDED]. Do not estimate effort or assign dates. If the order users go through the steps is unclear from the notes, say which order you assumed and ask me to confirm it.