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Best practices when updating a Flow used by a Power App

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This article describes best practices around updating Microsoft Flows used by Power Apps.

Applies to:   Power Apps
Original KB number:   4477072

Symptoms

After updating a Flow, calls to that Flow from Power Apps start failing.

  • If a new input is added to a Flow without a Power App being updated, the Flow will fail with an error message like:

    Unable to process template language expressions in action 'Send_me_a_mobile_notification' inputs at line '1' and column '1900': 'The template language expression 'triggerBody()['Sendmeamobilenotification_Text']' cannot be evaluated because property 'Sendmeamobilenotification_Text' cannot be selected. Please see https://aka.ms/logicexpressions for usage details.'.

    Screenshot of the error message when adding the new input to the Flow without updating the Power App.

  • If the connections required to run a flow change, an error complaining about connections should appear:

    In Power Apps, it may look like

    Screenshot of the error message complaining about the connections in Power Apps.

    Or in Flow

    Unable to process template language expressions in action 'Send_an_email' inputs at line '1' and column '1899': 'The template language expression 'json(decodeBase64(triggerOutputs().headers['X-MS-APIM-Tokens']))['$connections']['shared_office365']['connectionId']' cannot be evaluated because property 'shared_office365' doesn't exist, available properties are 'shared_flowpush'. Please see https://aka.ms/logicexpressions for usage details.'.

    Screenshot of the error message complaining about the connections in Flow.

  • If a response output is removed, Power Apps will treat the value as blank and the PowerApp will behave unexpectedly.

Cause

To invoke a Flow from Power Apps, Power Apps needs to know what inputs the Flow needs, what connections to supply to Flow and what outputs a Flow will return. Power Apps store this information in the definition of your Power App. Which creates a binding between a version of a Power App and the Flows used in it. Changing any of these three aspects of a Flow can break all previous versions of Power Apps that integrate with that Flow. To fix an affected Power App or to make use of one of these Flow changes, the Power App needs to be updated.

Types of changes most likely to break a Power Apps ability to call a flow include:

  • Adding a new Ask in Power Apps token.

    Screenshot of adding a new Ask in Power Apps token.

  • Adding a new connection. For example, by adding a new action from a Connector that wasn't previously used like the SharePoint Connector.

    Screenshot shows an example of adding a new connection.

  • Changing an existing connection. For example, changing an existing connection to a new connection.

    Screenshot of changing an existing connection in Flow.

  • Removing an output from a Respond to Power Apps action.

    Screenshot of removing an output from a Respond to Power Apps action.

Other changes to the inputs or outputs won't break the integration between Power Apps and Flow but will require the Power App to be updated so that it can use them.

Resolution

  • Changing a live PowerApp

    Once a Power App is published, it's always recommended to make copies of Flows used by the Power Apps to make any updates. Any update to a Flow referenced by a live Power App has the potential to break existing users. Don't delete or turn off the existing Flows until all users have been upgraded to the new published version of the Power App.

    Screenshot to make copies of the Flows used by the Power Apps by selecting the Save As option.

    In the new version of the Power App, reference the new Flows. When the new version of the Power App is published, users will start to use the new Flows with the correct inputs, outputs, and connections. Which will prevent Flow updates for new versions of Power Apps from affecting users of the existing version.

  • Changing a PowerApp development version

    While developing a Power App, making changes to a Flow not used by a live version of the PowerApp is easy. After making changes to the inputs, outputs, or connections of a non-published Flow, reselect the Flow from the Flows Pane.

    Screenshot of updating a Flow definition in Power Apps.

    It will update the definition of the Flow in the PowerApp validating that the correct input, outputs, and connections are used in the Power App.

    Users of the Power App won't begin using the new Flows until the Power App is published. So updating the existing Flow is ok until it's used by a live version of the Power App.