outlook.live.com/mail/0/

Hello, I have recently signed up to Microsoft 365 Apps for business account in the UK, but with my business email address. I am now signed into Microsoft 365 and clicked on the outlook live. My e-mails are sending but as "outlook_77C3BF8B3AE9****@outlook.com" on behalf of my email address, and when I send test emails to the account, they are not being received. My account shows my business e-mail address, but also shows this long outlook email. How can I solve this in my account?

I want to solve this before downloading the apps to my laptop. Thanks in advance.