How do you castle on this app??


You castle on the app the same way you should OTB. Grab the king, move it to a square either two to the right or two to the left, depending on which side you are attempting to castle on. OTB, you would then move the rook to the other side of the king; here, the rook moves automatically.
You can either click the king and the destination square or drag the king to the destination square.
tried all this before advice and since....still will not work...there is some nuance to this that I am missing..at this stage it is annoying me and I may have to abandon the app. but thanks for your input...I know...its always easy when you know how
Unlikely.
Make sure castling is legal. Post a game in which you couldn't castle and on which move. Make sure it is the king you are touching, and it is 2 steps.
You cannot castle when in check.
I am having the same problem - exactly. I have tried to castle when it is legal as directed above. Like the app otherwise. But this is a ‘deal breaker’ for me. Any suggestions?