Alan owns a shophouse unit and he uses it to sell antiques.

Alan and Charles are old friends and ex-business partners. Charles is retired but as a hobby, he regularly sources antique cameras for Alan who paid the market price for them. One day, he found a rare vintage Leica camera and brought it to Alan's shop on 20 September 2021. The same new shop assistant did not recognize him and rejected the camera. Incensed, Charles said: "Go tell your boss Charles came by with a rare vintage Leica cam that he has been looking for ages, and if he doesn't contact me soon, it may be too late to get it from me. But as he is my old friend, I give him one week (by midnight of 26 September) before I will sell it to another antique shop. The shop assistant left a note for Alan, who only read it on the evening of 26 September, and promptly sends an email to Charles stating that he will buy it and to contact him ASAP.However, Charles had already sold it to someone else on 24 September. Alan really wants the camera.

Is the statement from Charles an offer or invitation to treat? Can Alan sue Charles for selling the camera to another buyer?