Power Apps Flow Trigger Error: Expected String but got Null

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Posted on by MV-09090656-0

I'm trying to trigger a flow from a button in my Power App, but I keep getting the following error:

{
  "error": {
    "code": "TriggerInputSchemaMismatch",
    "message": "The input body for trigger 'manual' of type 'Request' did not match its schema definition. Error details: 'Invalid type. Expected String but got Null.'"
  }
}

The attachment field is optional, but even when no file is uploaded, this error still occurs.

Here is the code behind the button:

// Call the flow and store the result
Set(
    varResult;
    'Arbeidsrecht:Uitspraak'.Run(
        Coalesce(TextInput1.Text; ""); // required field
        {
            text_1: If(IsBlank(TextInput2.Text); ""; TextInput2.Text);
            text_2: If(IsBlank(TextInput3.Text); ""; TextInput3.Text);
            file: If(
                CountRows(BijlageVeld1.Attachments) = 0;
                {
                    name: "geen_bijlage.txt";
                    contentBytes: ""
                };
                {
                    name: Coalesce(Last(BijlageVeld1.Attachments).Name; "");
                    contentBytes: Coalesce(Last(BijlageVeld1.Attachments).Value; "")
                }
            )
        }
    )
);

// If a result is returned, reset the input fields
If(
    !IsBlank(varResult);
    Reset(TextInput1);
    Reset(TextInput2);
    Reset(TextInput3);
    Reset(BijlageVeld1)
)

What could be causing this error, and how can I ensure the flow accepts the input correctly even when no attachment is provided? With the help of ChatGPT I tried about 100 different formula's and none of the work.

Tnx!

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Building Power Apps

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StretchFredrik 3,395 Super User 2025 Season 2 on at

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Hello,

can you try the below code, and see if it makes a difference?

Set( varResult; 'Arbeidsrecht:Uitspraak'.Run( Coalesce(TextInput1.Text; Text("")); // required field { text_1: If(IsBlank(TextInput2.Text); Text(""); TextInput2.Text); text_2: If(IsBlank(TextInput3.Text); Text(""); TextInput3.Text); file: If( CountRows(BijlageVeld1.Attachments) = 0; { name: "geen_bijlage.txt"; contentBytes: Text("") }; { name: Coalesce(Last(BijlageVeld1.Attachments).Name; Text("")); contentBytes: Coalesce(Last(BijlageVeld1.Attachments).Value; Text("")) } ) } ) );

If my response solved your issue, please mark it as ✅ Accepted Answer and give it a like.

1 people found this reply helpful.

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MV-09090656-0 6 on at

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@StretchFredrik

Thank you for your reply. No it doesn't work. The code doesn't give an error, but the send button just doesn't work without attachment. If I add an attachment it does work.

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Power Platform 1919 1,894 on at

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Hi @MV-09090656-0,
Can you share the screenshot of the Power Automate flow trigger?
and can you check is the Field marked as optional?

click on Peek Code:

check for required field:

if required is [] means it is not expecting any required input

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MV-09090656-0 6 on at

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@Power Apps 1919,

Thank you for your response.

It is optional. Only the first field is mandatory.

The code:

{

    "kind": "PowerAppV2",

    "inputs": {

        "schema": {

            "type": "object",

            "properties": {

                "text": {

                    "title": "Uitspraak",

                    "type": "string",

                    "x-ms-dynamically-added": true,

                    "description": "Please enter your input",

                    "x-ms-content-hint": "TEXT"

                },

                "text_1": {

                    "title": "Opmerkingen",

                    "type": "string",

                    "x-ms-dynamically-added": true,

                    "description": "Please enter your input",

                    "x-ms-content-hint": "TEXT"

                },

                "text_2": {

                    "title": "Link",

                    "type": "string",

                    "x-ms-dynamically-added": true,

                    "description": "Please enter your input",

                    "x-ms-content-hint": "TEXT"

                },

                "file": {

                    "title": "Bijlage",

                    "type": "object",

                    "x-ms-dynamically-added": true,

                    "description": "Please select file or image",

                    "x-ms-content-hint": "FILE",

                    "properties": {

                        "name": {

                            "type": "string"

                        },

                        "contentBytes": {

                            "type": "string",

                            "format": "byte"

                        }

                    }

                }

            },

            "required": [

                "text"

            ]

        }

    },

    "metadata": {

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Power Platform 1919 1,894 on at

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Update 2:
When you have to send Optional Attachments , try the formula in this format. (Sample Call)
Attachment_Upload_Test.Run( If( CountRows(Attachments.Attachments) > 0, { file: With( {File_c: First(Attachments.Attachments)}, { name: File_c.Name, contentBytes: File_c.Value } ) }, Blank() ) )

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MV-09090656-0 6 on at

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@Power Apps 1919 Thanks, but that doens't work either. It is a different message however. Instead of missing string, it now says: "Expected object but got Null."

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Power Platform 1919 1,894 on at

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Hi @MV-09090656-0,
Sorry for the late follow up, can you please share where you are getting the error , is it in the trigger or any other action.

in my case:
i tried this . ( this is required as you cant send null to the create file action).
Pics:
Condition :

empty(triggerBody()?['file']?['contentBytes'])

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