Ask for the reason briefly
Illness, travel and work are normal reasons. You do not need proof for a short extension.
Check their progress
Look at what they have finished so the new date is realistic.
Apply your rule
Offer the standard extension, and decide who can approve longer ones.
Give a specific new date
Say the exact date access will end, not just a number of weeks.
Say what cannot change
If certificates or support end on the original date, mention it.
Mention a paid extension
If you charge for more time, say the price and how to buy it.