Emails in message queue but not sent

Hi there,
I'm running the nopcommerce(4.20) in azure. The emails in message queue are not sent.
And my email testing (Admin>Configuration>Email accounts) works fine but in the queue there are a lot of emails which have the status "not send".  It works only if i run the schedule task.
I'll be very happy if someone writes what the problem might have been caused by. Thanks in advance.

2 things need to be checked here.

1) Store configuration (Admin dashboard Configuration > Stores). Make sure that the store url and site url are identical.

2) Check error log.

mhsjaber wrote:

First one is check  and log error is :

SendinBlue error: Plugin not configured.
Nop.Core.NopException: Plugin not configured at Nop.Plugin.Misc.SendinBlue.Services.SendinBlueManager.CreateApiClient[TClient](Func`2 clientCtor) at Nop.Plugin.Misc.SendinBlue.Services.SendinBlueManager.UpdateContactAfterCompletingOrder(Order order)