We secure 0.3 MATIC or 0.02 ETH per link to cover gas on the basic (free) plan. The difference between the actual gas cost per particular link claim and this amount can't be refunded.
You can only refund the amount of tokens secured to cover the gas for the unclaimed links and distributed tokens.
I.e. you have created 10 links on Polygon and secured 0.3*10 MATIC to our contract at creation. 8 links were claimed by your users. 2 links are unused. You can refund 0.6 MATIC.
In the same dropdown menu where you've selected "Pause", select "Refund". This button will become active after pausing a campaign.
Sign the transaction, wait for it to get mined and receive your tokens
If you refund the sponsorship tokens and then unpause the campaign again, your users will still be able to claim assets in the links. However, they will see the screen that there is not enough tokens to cover the gas and be suggested to pay for the transaction themselves (see screenshot below)
Here is what your users will see if you'd unpause the campaign after refunding the sponsorship tokens