Unable to import certificate to APs

Hi, 

I'm trying to import a certificate to an AP. I'm following this guide:

https://docs.fortinet.com/uploaded/files/3309/Fortiwlc-sd-v8.2.4-config-guide.pdf

So basically I go Configuration > Certificates > AP Certificates, select the desired AP and click Import.

The steps are simple, but when I try to apply the certificate to the AP I see an error in the AP certificates list:

Cert-Installation-Failed

The certificate is valid and it was installed previously to one of the APs.

Trying to troubleshoot, I'm trying to install the certificate manually following this command:

ap import-cert ap56 Mycert  

but the syntax indicates that after the certificate name I need to enter URL from where the controller should download the certificate.

Now, when I try the IP address of the controller i.e. https://10.x.x.x it says value must be integer. I have also tried different values for that syntax like the server's URL, a fake url etc etc with no luck. 

I've been looking for examples of this command or what value should go there but I haven't found anything there.