If you can't log in although you are sure that you are using the correct login and password combination, please check the followings:
Are you trying to connect using the Moonworkers freelancer app?
Moonworkers avails an app for freelancers from the Google Play and Apple stores. This app is not for employees. Instead, use this link to connect to your employee's access: https://employees.moonworkers.co.uk/
Has your employer misspelt your email address?
Your employer may have used a mix of upper and lower cases when registering your email. This sort of spelling is not allowed on Moonworkers. Ask them to correct your email address.