Ethereum API Request Issue: Using Variables in Parameters
As an Ethereum developer, you’re likely familiar with the importance of using correct parameter names and data types in your requests. However, one common issue arises when working with variables that need to be passed as parameters. In this article, we’ll explore why your {{sellPrice}} variable is being rejected by the API and provide a solution.
The “Signature for this request is not valid” Error
When sending an API request in Postman or any other tool, you’re required to specify the parameter name (without quotes) followed by the data type (e.g., {{sellPrice}}). The exact syntax may vary depending on the API endpoint and its specific requirements. However, a common issue arises when variables are used without quotes.
The Problem with {{ }} Syntax
In JavaScript, template literals ({...}) and string interpolation (${...}) have different behaviors when it comes to variables. When you use {{ }}, Postman is interpreting the {} as the start of the variable name, which can lead to issues if the variable contains special characters or spaces.
For example, consider a request with a parameter like this:
LOCATION /api/price HTTP/1.1
Content-Type: application/json
{
"price": "{{ sellPrice }}",
"symbol": "{{ symbol }}"
}
If you use {{ }} syntax to pass the sellPrice variable, Postman will recognize it as a template literal and ignore it in the request body.
Why {{ }} is not valid
To fix this issue, you need to escape the ${} characters around your variable using double curly braces ({{{...}}}). This tells Postman that the following parts are placeholders for values:
LOCATION /api/price HTTP/1.1
Content-Type: application/json
{
"price": "{{ sellPrice }}",
"symbol": "{{ symbol }}"
}
Solution
To use your variable {{sellPrice}} in the request, follow these steps:
- Escape the
{}around your variable using double curly braces ({{{...}}}).
- Keep the rest of the syntax intact.
- In your Postman request body, replace
{{ }}with{{{...}}}>.
Here’s an updated example:
LOCATION /api/price HTTP/1.1
Content-Type: application/json
{
"price": "{{ sellPrice }}",
"symbol": "{{ symbol }}"
}
Tips and Variations
- If you’re using a template engine (like Handlebars or Mustache), you’ll need to use the
{{ variable_name }}syntax instead of{}.
- In some cases, you might need to use single quotes (
') around your variable name if it contains special characters. For example:
LOCATION /api/price HTTP/1.1
Content-Type: application/json
{
"price": "'{{ sellPrice }}'",
"symbol": "'{{ symbol }}'"
}
By following these steps, you should be able to successfully use your {{sellPrice}} variable in the API request parameters.
Conclusion
Using variables with special characters or spaces can lead to errors when sending requests in Postman. By escaping the {} around your variable using double curly braces ({{{...}}}>), you can ensure that Postman correctly interprets and passes your values as required.
