unable to change associated content type after setting content type as page layout in csom

Question

Below is my code

private void attachContentType(string siteURL, string path, string filename, ClientContext ctx, string folderName)
        {
            Web web = ctx.Web;
            Microsoft.SharePoint.Client.File home = ctx.Web.GetFileByServerRelativeUrl(web.ServerRelativeUrl + "/" + folderName + filename);
            ctx.Load(home);
            ctx.ExecuteQuery();
            home.ListItemAllFields["ContentTypeId"] = web.ContentTypes.GetByName("Page Layout").Id;
            home.ListItemAllFields["PublishingAssociatedContentType"] = web.ContentTypes.GetByName("Content Type Name").Name;
            home.ListItemAllFields.Update();
            ctx.ExecuteQuery();
        }

What I am trying to achieve is, set the type of the file to page layout, and set the associated content type to my custom content type.

This doesn't throw any exception, but when I edit the uploaded file it throws the below error

Failed to set value of the "Associated Content Type" column on the "Content Type ID" field type control

Answer 1

The format in PublishingAssociatedContentType should be ;#ct name;#ct id;#

Try below code:

var associatedContentType = web.ContentTypes.GetByName("Content Type Name");

String contentTypeAssociativeID = null;
if(associatedContentType != null)
{
    contentTypeAssociativeID = String.Format(";#{0};#{1};#", associatedCTName.Name, associatedCTName.StringId);
}

Web web = ctx.Web;
Microsoft.SharePoint.Client.File home = ctx.Web.GetFileByServerRelativeUrl(web.ServerRelativeUrl + "/" + folderName + filename);
ctx.Load(home);
ctx.ExecuteQuery();
home.ListItemAllFields["ContentTypeId"] = web.ContentTypes.GetByName("Page Layout").Id;
home.ListItemAllFields["PublishingAssociatedContentType"] = contentTypeAssociativeID;
home.ListItemAllFields.Update();
ctx.ExecuteQuery();

Set O365 PageLayout Associated Content type field