Log into your business Facebook profile.

Click the three dots in the grey rectangle on the right hand side of the page.

In the drop down, click Add Action.

Click Change Button.

Scroll down and click Contact Us and click Next.

Click Add website link, click Next.

Paste your Client Portal link, click Save.

Once saved, click on the same dots in the grey rectangle, again.

Click View As in the dropdown. You will now see the Contact Us button under your company page Facebook banner.