Trello Approval List Workflow
When a card is moved to an Awaiting Approval list, the flow launches a Power Automate approval to the assignee/owner, writes the decision as a card comment, and moves the card to an Approved or Rejected list. Adds governed, auditable approvals to a Trello board.
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Overview
This flow adds a governed, auditable approval step to a Trello board using the Power Automate Approvals engine. When a card is moved into an Awaiting Approval list, the flow launches an Approve/Reject request to the configured approver, writes the decision (and the approver's comments) back onto the card as a comment, moves the card to the Approved or Rejected list, and emails the approver a confirmation.
Why it matters: Trello has no native, auditable approval with assignment and outcome capture. This wraps cards in the Microsoft Approvals engine so every decision is tracked, attributed, and recorded on the card itself.
Ships Off - turn on by authorizing the three connections and setting the four list/approver env vars.
Use Case
Teams that run requests through Trello (content sign-off, purchase requests, change requests) want a real approval gate tied to a list, with the decision recorded back on the card. Move a card into the Awaiting Approval list and the approver gets a Power Automate approval; the outcome is written to the card and the card is filed in the Approved or Rejected list automatically.
Flow Architecture
Card Enters Awaiting Approval
Trello - OnNewCardInListV3Polls (every 3 min) for cards entering the list bound to flowlibs_ApprovalListId.
Initialize Config & Card Context
Initialize variable (x7)Binds board, approved/rejected lists, approver, and the triggering card's id, name, and URL.
Start Approval
Approvals - StartAndWaitForAnApprovalLaunches an Approve/Reject request to the approver and waits for the decision.
Check Approval Outcome
ConditionBranches on outcome == Approve.
Approved branch
Trello + OutlookComments APPROVED (with approver + comments) on the card, moves it to the Approved list (UpdateCard_V2), and emails an approval confirmation with the card link.
Rejected branch
Trello + OutlookComments REJECTED (with approver + comments) on the card, moves it to the Rejected list, and emails a rejection notification with the card link.
Environment Variables
| Schema name | Type | Default | Description |
|---|---|---|---|
| flowlibs_TrelloBoardId | String | REPLACE_WITH_TRELLO_BOARD_ID | Board the trigger polls and the comment/move actions write to. |
| flowlibs_ApprovalListId | String | REPLACE_WITH_AWAITING_APPROVAL_LIST_ID | The Awaiting Approval list that triggers the flow. |
| flowlibs_ApprovedListId | String | REPLACE_WITH_APPROVED_LIST_ID | Destination list when approved. |
| flowlibs_RejectedListId | String | REPLACE_WITH_REJECTED_LIST_ID | Destination list when rejected. |
| flowlibs_ApprovalDefaultApproverEmail | String | approver@yourcompany.com | Approver who receives the approval and outcome email. |
Connectors & Connections
| Connector | API name | Actions used |
|---|---|---|
| Trello | shared_trello | OnNewCardInListV3 AddCommentToCard UpdateCard_V2 |
| Approvals | shared_approvals | StartAndWaitForAnApproval |
| Office 365 Outlook | shared_office365 | SendEmailV2 |
Note — All connections are referenced as solution connection references; the flow is portable between environments as long as a connection is mapped at import time.
Customization Guide
Almost every realistic variant of this flow can be implemented by changing environment variable values. A few cases require small edits inside the flow definition — those are called out explicitly below.
- Per-card approver routing
- Replace the static approver with a member-to-email lookup (ListCardMembers -> map member id to UPN) so each card routes to its owner; fall back to the default.
- Multi-stage approvals
- Chain a second StartAndWaitForAnApproval for high-value cards (e.g. gated on a label) before the move.
- SLA / escalation
- Wrap the approval in a Do until with a timeout, or add a parallel reminder branch that re-notifies if not actioned within N hours.
- Re-entrancy guard
- Set an interim label (e.g. In Review) on first pickup and filter it out so a card lingering in the list is not re-submitted.
- Richer audit
- Log each decision to a Dataverse table or SharePoint list alongside the card comment for reporting.
Key Expressions
The flow is intentionally light on Power Fx / WDL gymnastics — the heaviest expressions are the branch-name concatenation and the approval outcome check. They are listed below in the order they appear in the flow.
EXPR.01Outcome
The approval outcome.
EXPR.02Branch test
True on approval.
EXPR.03Approver display name
Who actioned the approval.
EXPR.04Approver comments
Reviewer comments captured from the approval.
EXPR.05Target list (single-action form)
Resolves the destination list from the outcome.
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