With a very large (over 35000 variables/fields) and complex project (bilingual setup with lots of HTML commands and Spanish characters in the field descriptions and answer alternatives), I ran into the

Error in inherits(ds, "data.frame") : object 'ds' not found

error. I assumed that it had to do with non-ascii characters like in other issues and tried to isolate the error. I was not successful as the root of the error already lies in the first step using httr::POST (the command executes successfully but results in NA instead of comma-separated text.

I experimented a bit and realized that I could successfully download the metadata when using format = json instead of format = csv. I have implemented an option to choose json as the download format in redcap_metadata_read() in a fork of your repository: januz@518925c

Just wanted to let you know in case you would like to include this option in your package as well. Thanks for all your great work with this package!