Welcome to the community.
Have a look at your light and it must only be an entity not a device. This is a link to my sensor light blueprint FAQ but it is all the same. Click Here
If that doesn’t work then could you please provide us your YAML of the automation? This YAML code are the settings you have selected in the automation so I can help. To do this go into your automation, top right 3 dots, Edit in YAML, copy all the code, come back to the forum and in your reply at the top tool bar click on “</>” and paste code in there.
Blacky 