For once and for all Everton bought Dele (not loan) from Spurs but for nothing upfront with contingent fees depending on appearances (never met), a sell-on % and (we now know) a fee on contract extension/renewal.
With his contract with us now expired we would have to pay Spurs if we renew his contract. We are attempting to negotiate that away so we can offer him a new contract without paying a fee. Spurs will retain their sell-on clause (increased?) if we do.
It is an unusual deal but it not that hard to understand.