Hello Sasha Elezovski,

Thank you for your purchase. 

You need to check this redirect URI in your database and your Google project. To see if they are the same.   Please be careful when you update this table.

In your database, you have to find wp_options table:

In your case it is possible for it to have different prefix but it will end like your_prefix_options. 

Then you have to find the option name amelia_settings in this table.

When you find that you have to edit that property and to find there the string redirectURI , so you will probably find something like this:

 It needs to have the escape characters " \ ", so don't remove those. Simply check if the URI is the same as in Amelia/Google Calendar Settings and if it isn't, please modify it here. Please note that if you use https you will need to update it also in redirectURI option.

When you finish with this please check if the URI is the same in the field Authorized redirect URL's on "Create OAuth client ID" section in your Google credentials section.

Sometimes this issue comes up, mostly when there is a security involved so there is a mismatch in http/https and sometimes users don't press Enter (after typing the domain in the required field  in 'Authorized redirect URIs') to add it before clicking on 'Save' in the Google Cloud Platform. So the field stays empty and causes the issue. This is why you need to go on in the database and change it manually. 

Please let me know if this helped!