Welcome to the ODK forum, @Dolapo! We're glad you're here. When you get a chance, please introduce yourself on this forum thread. I'd also encourage you to add a picture as your avatar because it helps build community!
It sounds like you may have an issue with your syntax. The XLSForm documentation is here. When converting your form with XLSForm Online it should give details in the error message about what went wrong.
Can you share the .XLSX
version of your form here? If you're using ODK Build you can got to "File" and then "Export to XLSForm".