Power Automate allows you to use expressions in dynamic content, conditions, and actions to process data. However, incorrect syntax can cause the following error:
“Invalid Expression Syntax – Error due to incorrect syntax in the formula or expression.”
This issue occurs when an expression:
- Uses incorrect function syntax (e.g., missing brackets, extra commas).
- Has mismatched data types (e.g., passing text where a number is expected).
- References non-existent variables or fields.
- Contains extra or missing quotation marks.
2. Common Causes of Invalid Expression Syntax Errors
| Cause | Description | Example |
|---|---|---|
| Missing or Extra Parentheses | Not closing brackets properly in a function. | add(2, 3 instead of add(2, 3). |
| Incorrect Function Usage | Using the wrong number or type of arguments. | substring('hello', 2, -1) (negative length invalid). |
| Invalid Quotes | Using incorrect single/double quotes in strings. | "Hello" (correct) vs. 'Hello" (incorrect). |
| Mismatched Data Types | Passing a number to a function that expects text. | toUpper(123) instead of toUpper(string(123)). |
| Undefined Variables or Fields | Using variables that don’t exist. | variables('myVar') when myVar is not defined. |
| Incorrect Array Indexing | Accessing an array with an invalid index. | items('Apply_to_each')[0] (should be without [0]). |
3. Step-by-Step Troubleshooting Guide
Step 1: Identify the Expression Error
- Open Power Automate (https://flow.microsoft.com).
- Navigate to My Flows and open the flow with the error.
- Click Run History and find the failed run.
- Expand the failed action and locate the Expression that caused the error.
- Read the error message carefully—Power Automate often highlights the problem.
Example Error Message:
"InvalidExpressionError: The expression is invalid. Unexpected token ' , ' at position 10."
This suggests an issue with extra commas in the expression.
Step 2: Check Function Syntax
Ensure the function follows the correct syntax.
Common Functions & Correct Syntax:
| Function | Correct Usage | Incorrect Usage |
|---|---|---|
| add() | add(5, 3) | add(5, 3, ) (extra comma) |
| concat() | concat('Hello', ' World') | concat(Hello, 'World') (missing quotes) |
| substring() | substring('PowerAutomate', 0, 5) | substring('PowerAutomate', 0) (missing length) |
| if() | if(equals(2, 2), 'Yes', 'No') | if(equals(2, 2) 'Yes', 'No') (missing comma) |
Example Fix:
Incorrect:
add(5, )
Correct:
add(5, 2)
Step 3: Fix Missing or Extra Quotes
Power Automate expects single quotes inside expressions for text values.
Correct Usage:
✔ concat('Hello', ' World')
✔ if(equals(variables('Status'), 'Completed'), 'Done', 'Pending')
Incorrect Usage:
✖ concat("Hello", " World") → Use single quotes
✖ if(equals(variables(Status), Completed), Done, Pending) → Quotes missing around text values
Example Fix:
Incorrect:
(Hello, 'World')
Correct:
concat('Hello', 'World')
Step 4: Convert Data Types Properly
Some functions require specific data types.
Use string() to convert numbers to text:
✔ toUpper(string(123)) → Converts 123 to "123".
Use int() to convert text to numbers:
✔ add(int('5'), 10) → Converts "5" to 5 before adding.
Incorrect Usage:
✖ toUpper(123) → Fix by converting to a string
✖ add('5', 10) → Fix by converting ‘5’ to int
Example Fix:
Incorrect:
add('5', 10)
Correct:
add(int('5'), 10)
Step 5: Ensure Variables and Fields Exist
If you reference a variable or dynamic content field that does not exist, Power Automate throws an Invalid Expression Syntax error.
Check if the variable is defined:
✔ variables('myVar') – Ensure myVar is created in Initialize Variable action.
Check if dynamic content exists:
✔ Use triggerOutputs()?['body']['fieldname'] to reference fields safely.
Example Fix:
Incorrect:
variables('MissingVar')
Correct (if defined):
variables('ExistingVar')
Step 6: Verify Array Indexing
When working with arrays, indexing must be correct.
Correct Usage:
✔ first(variables('myArray')) → Retrieves the first item.
✔ last(body('Get_items')?['value']) → Retrieves the last item from a SharePoint list.
Incorrect Usage:
✖ items('Apply_to_each')[0] → Wrong format for Power Automate loops.
Example Fix:
Incorrect:
items('Apply_to_each')[0]
Correct:
items('Apply_to_each')
Step 7: Test the Fixed Expression
- Go to the Flow Designer in Power Automate.
- Modify the expression using the correct syntax.
- Click “Test” and run the flow manually.
- Check if the error disappears.