The both are the same, but mosly use OK to say something very forcefully or you are not really agree but Okay to show your interest or your agreement in some point.

They are pronounced the same in speech, so no differences there. But in writing, you will only see OK in unproffessional settings. Text, emails to close associates/ friends, etc. Otherwise, default to okay to be safe. OK was the original BTW (by the way) before the internet and texting began abbreviating everything Bbl Omw Omg Imo Smh Afk Etc. ;-P

There is no difference between the two in context.

both are okay/okay

@Chiris, thanks.