I've explained this before, Betis were adamant about getting the €75 million (which they then dropped to €70 million) that they agreed with the player. That was their de facto buy-out clause, one which more resembles how these things work in England and elsewhere. Spurs would still have had to do business with Betis, iron out the nuts and bolts, like payment schedules and so. That isn't how a clausula de recisión works - when this is triggered the buying club has no contact with the seller, who has no say whatsoever in the matter. The buyer does business directly with the player and the Spanish League, who hold all contracts. Spurs would put €100 million (plus VAT) in Lo Celso's account, he would then transfer that to LaLiga who would hand over a terminated contract to Gio. At that point he is a free agent and can then sign for Spurs.
So our serious negotiations with Betis began at €75 million, not at €100 million, as they were prepared to both (a) not try to hold on to the player, offer them higher wages etc and (b) do business with Spurs, unlike the Griezmann case I mentioned.
One case where we sort of paid the clausula de recisión but actually didn't was that of Soldado. He had a fairly low clausula - €30 million - and two suitors, Spurs and Liverpool. The latter were prepared to pay the clause as I set out above, but the player preferred to come to Spurs. Valencia, who were in administration at the time, with their affairs handled by a creditor bank, knew they would get their €30 million one way or another. All attempts by Franco Baldini to get them to bring the price down met with a firm no - why should they? They'd get it from Liverpool. So in the end, we managed to negotiate staggering the payments over two years (we initially wanted three). It worked out the same as paying the clausula although we did our business with Valencia, not LaLiga, and so it was registered as a transfer, not a buy out