The trial for Vegas Pro 18 has not been available from MAGIX since August last year, and if registered at the time has probably long since expired.
The best thing to do is to try the trial version of the current version of Vegas Pro 19 - https://www.vegascreativesoftware.com/us/vegas-edit/ - scroll down to the bottom of the page and click on the 'Free Trial' button.
Please note that this is a peer to peer forum and no-one on the forum has your registration/activation code.
@Christopher-chris This is a user forum, not sales support. If you got the registration email with the license number after you bought Vegas 18 and succeeded in registering it, the license number is also in your online Magix account. You can log into your Magix account and copy the license number and write it down if you no longer have the original email. The license number and your email address is all that is needed to activate Vegas.
If you never got the email and thus could not register the license, you need to contact sales@magix.net ... best to send them your Magix order number and order date so they can track it down. If you don't get an email response from Magix within a day or 2, you may need to create a temporary gmail or outlook mail account to receive email from them.
Make note that online scammers are offering VP18 for $20-30, and delivering only an old trial version without a legal registration pathway. If this is the case, you've been scammed.
Here is the download site for the current Vegas Pro 19 trial from Magix.