Claire went through a rough patch where she refused to take a nap (even though she'd be completely exhausted). So I started bribing her with "play doh surprise eggs." If she took a nap, she'd have a surprise egg waiting for her when she woke up!
They're plastic containers that you put a toy or a treat in. I'd use fruit snacks, a lego mini figure, a shopkins character. etc. Then you cover it with play doh and make a fun design.
It got to the point that Claire would ask to take a nap! Then she'd want to make her own!
Hooray for surprise eggs!