Hi, welcome to the forum.
It looks like you are missing that file dailyActivity_merged but there is not enough information that I, at least, can even make a guess why. That path_to_file looks suspicious and I think you have the syntax wrong.
It looks like you are trying to read in a .csv file and either the file does not exist or your path is incorrect.
What we need is a good bit of your actual Rmarkdown code. We don't need to see any of the actual text body. You can just throw in some random text as filler if you want between the code sections
What we need is the YAML (header information) and any R sections up to the R section where you are getting the error.
Copy the code and paste it here between
```
```
This should give us a nicely formatted output to work with.
Just for general information this may be helpfull though I am not sure it is directly applicable here https://forum.posit.co/t/faq-how-to-do-a-minimal-reproducible-example-reprex-for-beginners/23061