Problem uploading R package to repository generated using R package "drat"

Question

I want to upload the R package BOLTSSIRR to a repository generated using the R package drat. BOLTSSIRR is not my own package, but I need to upload it to a drat repository, because my package uses the BOLTSSIRR package and I want to upload my package to CRAN.

I did manage to upload the R package to drat, but it seems in the wrong directory. Here is the package: https://github.com/RomanHornung/drat

After listing BOLTSSIRR under Suggests: in the DESCRIPTION file of my package and adding Additional_repositories: https://github.com/RomanHornung/drat to the DESCRIPTION file as well, I ran R CMD check --as-cran on my package, but I got the following:

* checking CRAN incoming feasibility ...Warning: unable to access index for repository https://github.com/RomanHornung/drat/src/contrib:
  cannot open URL 'https://github.com/RomanHornung/drat/src/contrib/PACKAGES'

Suggests or Enhances not in mainstream repositories:
  BOLTSSIRR
Availability using Additional_repositories specification:
  BOLTSSIRR   no   ?
  ?            ?   https://github.com/RomanHornung/drat
Additional repositories with no packages:
  https://github.com/RomanHornung/drat

I'm not really familiar with GitHub. A step-by-step instruction would be greatly appreciated, but any other help as well!