Error in R using lmer: boundary (singular) fit: see ?isSingular

I am an undergraduate student trying to use the function lmer to create some models in R and I keep recieving this error message:

</> boundary (singular) fit: see ?isSingular

I am using dummy variables and so perhaps the package doesn't like my dummy variables, but I'm not sure. I've been looking online other places and once website suggested that "the model is likely overfitted and/or suffers from numerical stability issues". Could this be the case? What should I do in order to properly build my models? Thank you for the help!

Hi!

To help us help you, could you please prepare a reproducible example (reprex) illustrating your issue? Please have a look at this guide, to see how to create one: