Selenium: Unable to interact with element within fieldset tag

I am creating automation testscipt for a webapps using angular to develop frontend. There is a form with multiple input field inside a fieldset tag. I use Chrome DevTools to find xpath of the above input field but when run the script with my framework, webdriver cannot find the element with my xpath. Webdriver can click on the fieldset tag but cannot interact with any element inside the fieldset tag. I try debugging and put breakpoint at the step which input text to the input field but it doesn’t work. Please let me know what’s happen with the element inside the fieldset tag! Thanks a lot!