Hello Mike.

This usually happens if the purchase code is (for some reason) saved with a space in the database. So, even though it looks normal, and it is saved successfully in the plugin, it's saved with a space in front or after the code in the database.

If you know your way around the database, you can check this. Activate the code, then access your database via PHPMyAdmin (or some other tool), access the wp_options table:

It is possible that your prefix is not "wp_", but something else, so if that is the case, please look for "your_prefix_options" table.

When you access it, you can search through the column "option_name". Search for the term "amelia_settings":

The search will return only one row, and you need to edit it:

In "option_value" column, look for "purchaseCodeStore":

I don't have a purchase code saved in my local installation, but you'll see it like this:

In this example, there is a space between the last character and the closing quote, so after it's deleted the plugin should not deactivate the purchase code every time you attempt to update it. 

My advice would be to copy the entire purchase code section into a text editor. When I copied what you saw in the screenshot above, this is what I got:

"purchaseCodeStore":"XXXXX-XXXXX-XXXXX-XXXXX-XXXXX "

So, even though it's not obvious in the database, it shows there's a space in a text editor.

I hope that helps.