The main mistakes are with your punctuation. Always leave a space after a comma or a full stop and never put a space before a question mark.

Dear Sir/Madam, I have been invited to the next stage of the assessment; however, I cannot access the Online Immersive Assessment page. I have tried using both the Google Chrome and Firefox browsers. Could you please tell me how to solve this problem? Thank you for your time. Best regards, Cong H I have made it slightly more formal by adding "however" instead of "but" and replacing can't with cannot. This is because you want to be super polite in the interview process, and being informal is less polite. Being formal is more polite.