The Spurs can waive Lonnie Walker and free up enough cap space to make a max offer to DeAndre Ayton. The Suns can match that offer and keep Ayton, but that will likely result in a poor working relationship between Ayton and the Suns organization. Ayton and the Suns already have a tenuous relationship making it very likely that they part ways this offseason unless the Suns give Ayton a max offer (which the Suns are very reluctant to do as that will put them into the luxury tax).
A sign and trade can work well for all teams involved.
Suns does a S&T with Ayton getting about $28-30 million and going to the Spurs.
The Suns would get Jacob Poetl, Chris Boucher (S&T $10 million) and Malachi Flynn.
The Raps would get Devin Vassell from the Spurs.
The Suns do this because it lowers their overall team salary, gets them out of the Ayton situation, whilst landing them a center (Poetl) who will work just as well as Ayton in their system (ie. pick and roll, excellent defender), a power forward (Boucher) who is a good rim protector and can shoot the three, and a backup point guard (Flynn) who should also work very well in the Suns system as his strength is in the pick and roll.
The Spurs get a future All-Star in Ayton whilst giving up a very good defensive center (Poetl) and a promising young guard (Vassell).
The Raps get a guard (Vassell) who should fit nicely in their switch everything defense who is also a capable shooter. Flynn is a good prospect, but his playing style doesn't work in the Raps system. Boucher is an excellent fit in the Raps system, but Achiuwa is developing nicely and can fill the void left by Boucher.