Sharepoint Designer 2013 Cannot access Site - No permissions

Hi Antoine-BOA,

If you are using SharePoint Designer 2013, please confirm if the issue happens in all SharePoint sites or a specific SharePoint site.

The issue may be related to some scenarios, I’d like you to make sure that you have tried the following methods. If you haven’t tried some of them, try them to see the outcome.

1. Make sure that the log-in account in SharePoint Designer 2013 is the work and school account. If no, switch the account to see the outcome.
2. Use Windows Explorer to open these 3 locations and delete all the files below. Then reboot SharePoint Designer 2013 to see the outcome.

%APPDATA%\Microsoft\Web Server Extensions\Cache
%APPDATA%\Microsoft\SharePoint Designer\ProxyAssemblyCache
%USERPROFILE%\AppData\Local\Microsoft\WebsiteCache

3. Some such issues may be related to the custom script feature in the affected site is not turned on. I suggest you do the following and then re-open the site in SharePoint Designer 2013 to check the outcome.
a. Download the SharePoint Online Management Shell from the article .

b. Connect to the affected site via the SharePoint Online global administrator account with the following commands.

$adminUPN="<the full email address of a SharePoint Online global administrator account, example: jdoe@contosotoycompany.onmicrosoft.com>"

$orgName="<name of your Office 365 organization, example: contosotoycompany>"

$userCredential = Get-Credential -UserName $adminUPN -Message "Type the password."

Connect-SPOService -Url https://$orgName-admin.sharepoint.com -Credential $userCredential

c. Type Set-SPOsite <SiteURL> -DenyAddAndCustomizePages 0 to turn on the feature.

For your reference: Connect to SharePoint Online PowerShell

Turn scripting capabilities on or off

Thanks,

Cliff