The current version of Adobe Photoshop does not use a key or serial number. You have to sign in to your Adobe account, download the file, and sign in after installing. A computer restart may be necessary.
If you purchased a key, it was not from Adobe.
You need to provide some more detail. The only Photoshop version sold by Adobe now is Photoshop CC2018. There is no "key" for this - that ended many years ago. Today you sign in with a username and password.