Advice on getting our cat to use the catflap

[Hecksonaplane]

Just that really, we've had him a couple of years but never used the flap.
We have a couple of days planned away and thought actually it would benefit him to use it rather than wait for the sitter.
We have just managed to get him through enticing him with beef, otherwise he just sits and mews outside the door. Inside he just sits waiting.
I know it will take time but is there anything I can do to encourage him?
He's rather large and watching him slowly go through it in rather an exaggerated fashion is slightly amusing but I do want him to be comfortable (he won't get stuck it is definitely big enough) There is a step on the other side so no drop or anything.

Any ideas?

We had to prop it open for a couple of days to get our —rather dim— cat to go through it at first, then when he was happy using the hole we closed it and kept pushing him through with the aid of treats. He got it eventually!

good idea to prop it open!

I will give that a go. I tried to help him through but he dashes off and goes limp on the ground or tries to wait for you to open the door then dashes in.

Am i looking at days or weeks? He does amuse me