Writing for a client, a brand or a brief adds pressure, and pressure freezes words. A few ways through it:
Know the brief cold. Read it twice. Know the scene, the audience and the goal. Most blocks are really missing information.
Outline first. Bullet the story, the hook and the turn before you write a line. A roadmap beats a blank page.
Borrow the voice. Study the references in the brief, write a few lines in that voice, then make it yours.
Set a timer. Twenty-five minutes, no stopping, no editing. Then a break. Repeat.
Change rooms. Walk, switch spaces, step away from the screen.
Talk it out. Bounce the idea off a collaborator. Saying it out loud often finds the line.
Every writer hits the wall. The ones who get placed are the ones who keep writing.