Create a Sharepoint anonymous link using REST api - sharepoint

Question

I have a PHP application where I retrieve the documents from Sharepoint and display into a list where users can click to see/download the file.
Currently I'm linking to the Sharepoint URL which is protected by login. I need to link to a link that can be accessed by anonymous users.
I can create a share link using the Sharepoint interface and I see in the network tab (google console) that a POST request to https://myclient.sharepoint.com/sites/CustomerPortal/_api/web/Lists(#a1)/GetItemById(#2)/ShareLink?#a1=%27%7B11CD851B%2D1385%2D43DA%2DBB41%2D132AFAAA0927%7D%27&#a2=%274620%27 is made.
When I try to perform the same request via Postman I get the following error:
{
"error": {
"code": "-1, Microsoft.SharePoint.Client.InvalidClientQueryException",
"message": {
"lang": "en-US",
"value": "The expression \"web/Lists(#a1)/GetItemById(#2)/ShareLink\" is not valid."
}
}
}
I tried to create an anonymous link using the endpoint: https://myclient.sharepoint.com/sites/CustomerPortal/_api/SP.Web.CreateAnonymousLink
with the following JSON body:
{
"url":"http://myclient.sharepoint.com/CustomerPortal/Folder/file.pdf",
"isEditLink":"true"
}
and the response I get is:
{
"error": {
"code": "-1, System.InvalidOperationException",
"message": {
"lang": "en-US",
"value": "Operation is not valid due to the current state of the object."
}
}
}
How can I create a anonymous link using REST API? Is it possible? Is there any configuration that my client needs to do on Sharepoint side?
Thank you.