Ok,so I made this female sim for my lonely little male sim,and i used cheats to max out the relationship bar,and she does like my sim's appearance,but for some reason whenever he flirts with her he gets rejected.
And it's happened all the time.
Any tips or cheats?

I did this with another household too and it worked completely fine,so is there a bug or something?

They may not be compatible. Their sign, likes and dislikes and aspirations need to match enough for them to like each other. Use the 'ask' options for 'do you like what you see, what do you want, and any others that may give clues. Other players will probably have more or better suggestions.

I've tried it and it still doesn't work
Mods anyone?

I'm assuming you've given them both a 100/100 relationship not just your controllable sim?
If not set both at least 70/70 and try again.
If so start with friendly interactions and make them get the friend, best friend and BFF tags. Once those tags happened check what their chemistry is, if they have zero or one bolt then have your controllable sim charm your uncontrollable sim it will trigger a crush,a boost to their chemistry and then all your romantic actions should be accepted. If they have two or three bolts they should accept anything now the tags are set and immediately fall in love on the first romantic interaction.

Have both selectable and the one who rejects the other have that one do the flirt action and see what happens.

Thanks,that worked