First thing to check is the expiry. Quotes carry a validity period, and once it's passed, accepting is blocked on purpose. Open the job, extend it or resend, and the link works again.
Second: make sure they've got the whole link. A long URL broken across two lines in a text message is the commonest cause of a "broken" link.
Failing that, download the PDF and send them that while it's sorted out — and email hello@gaffermate.co.uk so somebody can look at the actual link.
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