groupID (int): This param limits the list to series from a given group.
Example query:
https://api.countrysidebible.org/series/?groupID=4
This will return a list of all series related to group 4. If you would like to include series from more than one group, you can concatenate IDs with a + delimiter.
Example query with multiple groups:
https://api.countrysidebible.org/series?groupID=19+20+22
The full list of groups is available here: