Hi Madhumitha, have you checked the logs to see if there is any information about the error displayed there? If the microflow is triggered from a button, check if the microflow setting is set to asynchronize call. If all of this doesn't help, then it might be worth it to debug the microflow and see what goes wrong.
Try to check logs in console. Mostly it happens when we use substrings. Check in the microflow whether you are using null conditions or not.
As others have mentioned, check the error logs. You should find a message (probably in red if running locally) that will say what happened. When we know what happened, we can work out how to fix it. It is usually a piece of data in the wrong format or with an unexpected value that you need to handle.