Computer specification and program version, see this topic for what is required and please quote processor and graphics card make/model in full - I would suggest you put this information in your profile signature so we do not have to keep asking for it.
Are you getting any error messages - if so what do they say - a screenshot would be best.
Do you have a serial number, begins with P3- followed by 5 sets of 5 numbers, or voucher code usually letters and numbers?
If you have a P3-serial number did you try copy and pasting the whole serial number including the P3 ?
I'm also getting an activation error after purchasing Movie Studio 2022 today. I get the green check mark next to the license when pasting it in. If I remove a couple digits, it goes away then type them back and I get the green check mark again so it looks valid on first glance. You can see in my screenshot, I have both green check marks for license and my email.
While the serial number is in the correct format - ie you are getting the green check mark, the error message suggests the issue is the serial number is not the correct one for the product you are trying to activate ie you have installed or purchased the wrong product.
Check the email confirmation for which product you purchased.