Upgrading Umbraco V13 to V15 - Backoffice ambiguous error

Trying to upgrade a project to Umbraco V15

updated all the package versions in the csproj file to most current version available

“Umbraco.Cms”, “Umbraco.Forms”
“Umbraco.Cms.Core”, “Umbraco.Cms.Infrastructure” to 15.1.1

“Umbraco.Forms.Deploy” , “Umbraco.StorageProviders.AzureBlob” and
“Umbraco.StorageProviders.AzureBlob.ImageSharp” to 15.0.0

when rebuilding the project I’m getting the following error

The call is ambiguous between the following methods or properties: 'Umbraco.Extensions.UmbracoApplicationBuilderExtensions.UseBackOffice(Umbraco.Cms.Web.Common.ApplicationBuilder.IUmbracoApplicationBuilderContext)' and 'Umbraco.Extensions.UmbracoApplicationBuilderExtensions.UseBackOffice(Umbraco.Cms.Web.Common.ApplicationBuilder.IUmbracoApplicationBuilderContext)'

on the AddBackoffice(), UseBackoffice() and UseBackOfficeEndpoints()
in the startup file

ideas?

please and thank you.


This is a companion discussion topic for the original entry at https://our.umbraco.com/forum/115182-upgrading-umbraco-v13-to-v15-backoffice-ambiguous-error