@HTRSGF said:
Api Key refresh
I'm new to programming and I'm building my first server application.
I don't really understand how the data acquisition process works.
I have an api key that I insert into the query string to get data from your service, and everything works fine,

Good.

but suppose a situation occurs when the api key of my application is either lost,
or accidentally changes its value,
or something else happens to it, and I get an Invalid API key error.
How can I handle this error on my server?

I don't know if I understand these possibilities well, but...
Fix your server by entering your correct API Key.

When I make a request for a new key and try to use it in requests, it doesn't work because my old api key is still active,

When you made the request for a New API Key, I assume you asked to regenerate your key, where/how did you receive this new key?
When your original API Key is regenerated it automatically stops working and the new one starts working.
So the scenario/plot you described doesn't make sense.

but what if I don't have access to this key and can't get the data.

On your profile page you will only find the new one.
https://www.themoviedb.org/settings/api

Do I really need to temporarily suspend the operation of my server until I go into my account settings and manually take the key from there?

If your API Key is not valid, you need to regenerate it and receive the new one.
This new one can be used on your server.

Before requesting a new API Key, or as we call it here, asking to Regenerate your API Key, do a test to check if it is in fact not working.
Go to this page: https://developer.themoviedb.org/reference/authentication-validate-key
Check if the "Authorization Header" option is set to "Access Token Auth", click "Try it!" and see the answer below.
If the answer was 200, your API Key is valid. You can continue using it.
If the answer was 401 then ask to regenerate your API Key.

This may be a really strange question, but I really don't really understand it, since this is my first serious interaction with an external api.
Moreover, as I understand it, the application key that I have in my account settings may expire, then what should I do.

application key ?
I assume you are referring to your API Key provided in your profile.
https://www.themoviedb.org/settings/api

It never expires. There is no expiration date.
Mine has been true since the beginning, about 8 years ago.
Your API Key may become invalid for a few reasons. For example:

• Internal defect here at TMDb
• Abusive use of your API Key

If someone has access to your API Key and, for example, uses it in a DDoS attack on TMDb servers, it could be invalidated.
Or if it is used on a film and series piracy website.

I think I'm finished now.

Thank you so much for your help and response, sorry for taking so long to respond. I have already managed to figure out that the keys that I received through the api are not the secret api key that is used by my application, but the request api key. Before that, I did not understand that there are different types of keys and tokens, and they are used for different purposes. My question was a little silly, but it couldn't be otherwise, since this is my first experience interacting with the api. Thank you again for giving me a little of your attention and time, yours sincerely, anonymous.