API does not support long list of SSH keys

I'm trying to get all the SSH keys associated with my (automation) user with the following in mind:

• this user is not admin.
• There is a very long list of SSH keys (>1000)
• I'd like to delete the stale keys - but for that I need the key ID (as per https://docs.gitlab.com/ee/api/users.html#delete-ssh-key-for-given-user)
• I'm using CE 11.5.4 (but we will update to 11.7.0 today)

The command I'm using is (as per https://docs.gitlab.com/ee/api/users.html#list-ssh-keys)

curl -s -H "PRIVATE-TOKEN:<MYTOKEN>" https://gitlab.sas.com/api/v4/user/keys

--> This only gives the first 100 keys

I've also tried

curl -s -H "PRIVATE-TOKEN:<MYTOKEN>" https://gitlab.sas.com/api/v4/user/keys?per_page=1000

--> This gives the first 100 keys

I've also tried

curl -s -H "PRIVATE-TOKEN:<MYTOKEN>" https://gitlab.sas.com/api/v4/user/keys?per_page=100&page=2

--> This also gives the first 100 keys (the same than above)

So far, i didn't find a way to access the other keys