Hi @Jaganath Kumar
Welcome to Microsoft Q&A platform and thanks for posting your question here.
The reason why '=' is being converted to '%3D' in your external API call using data flow is because '=' is a reserved character in URLs and needs to be URL encoded. When a URL is encoded, special characters are replaced with a percent sign (%) followed by a two-digit hexadecimal code. In this case, '=' is being replaced with '%3D'.
In your case, the value of the query parameter is "customer Number=234567". To correctly encode this value, the equals sign needs to be replaced with '%3D'. This is why you are seeing the encoded value of "customerNumber%3D234567" in the ADF data preview output.
This behavior is expected and is done to ensure that the URL is correctly interpreted by the server.
Reference
https://learn.microsoft.com/en-us/azure/architecture/best-practices/api-design#urls
I hope this information helps you. Let me know if you have any further questions or concerns.