License Key Problems

Hello I have problems very often to activate the plugins with the activation codes, I followed the procedures indicated in other Threads but I continue to encounter problems, obviously not only a damage of time but also financial since I buy these licenses.

I proceeded with the change from Server to Server. Now I don't get the error code anymore but I get another warning:

Could not be saved. Please contact Support if you continue to experience this issue.

The same goes for the theme I have on the website. It does not let me activate it.

How can we figure out what the problem is?

Hello.

Did you wait 30 minutes after the whitelist unlock?
What is the plugin?

Bye!