I've just read that substack.
Sykes is hissing mad. He has been championing "Megxsin" - very recently arguing that the king was damn-well going to have the Sussexes back in, regardless of what W , the media or the population of the UK thought, and the up-coming visit was proof of that.
Never mind blowing up chances of reconciliation with his dad, H has blown up a relationship with an important ally.
On another aspect of all this, I think in retrospect, we'll see that BP have played a blinder again. They have said very little officially - only confirming that the King has a standing offer to H to stay in a royal residence, and denying that the King had offered to pay for beefed-up security on this visit. Other than that, they've let the Sussex PR knock themselves out with ever-more detailed claims and statements, which they're now rowing back on.