To add a digital signature block to your proposal, just click the green block that says 'Add to this Page' on the right of any page. Once you’ve clicked that, a sidebar will appear showing you all of the things you can add. 

Then click 'Digital Signature'.

This will add a digital signature section to your proposal. You can only have one per proposal, so if you added one already, then you'll see a message to let you know that you can't add another one without removing the other.

You'll notice that the {{first_name}} and {{surname}} merge tags are in the acceptance text by default. You don't need to do anything with these as they will be automatically replaced with your client's name when they open the proposal.
Bear in mind you also won't see these replace on the proposal preview, because it's not tied to a specific recipient.

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