Hello Faramarz. It is an authorization issue. As I understand, you use a custom credentials API key. Please follow these steps:
- ensure that your Microsoft 365 account's password contains only letters and numbers, if necessary, change the password;
- for the account, you should either disable multi-factor authentication or create an app password, the latter should contain only letters and numbers;
- create a new API key for Actions in a Plumsail account using the full login in format user@tenant.onmicrosoft.com and the password;
- in the failed flow, create a new connection for Plumsail Actions using the newly created API key, ensure that it is selected for the action;
- save and test the flow by clicking the Test button, before running the flow, ensure that the proper connection is selected.
Please let me know whether it helps.